Rock and Soil Reinforcement

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Atlas Copco

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Rock & Soil Reinforcement third edition

www.rockreinforcement.com

Rock & Soil Reinforcement

Atlas Copco supplies the widest range of advance cost-efficient rock reinforcement solutions for mining and tunnelling, including fully-mechanized Boltec rock bolting rigs, Swellex rockbolts, and MAI self-drilling anchors. Each and every product has been designed to help maximize your tunnel advance and minimize costs per drilled metre – and always with the highest level of safety in mind.

www.atlascopco.com Printed matter no. 9851 6283 01b

Find out more at www.atlascopco.com and select “Country”. Or give us a call. We’d be happy to listen to your requirements, and even happier to meet them.

Third Edition

Atlas Copco MAI Phone: +43 4245 65 16 60 Fax: +43 4245 65 16 68 00

Because we’re a global organization, we have the resources to be truly local.

Talking Technically Case Studies Product Specifications a technical reference edition

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Contents Foreword 2

Foreword by Federico Scolari, Vice President Marketing, Atlas Copco Craelius.

Talking Technically 3 5 7 11 13 15 17 19 22 24 28 33 35 38 41 43 45 47 51 55 59 61

Innovative Solutions for Rock & Soil Reinforcement Investing in Rock Reinforcement Controllable Rock Reinforcement Swellex Manganese Offers Improved Work Index Swellex Premium Line Hollow-Core SDA System Atlas Copco MAI Self Drilling Anchors Symmetrix For Large Holes Sacrificial Drill Bits Mechanized Bolting Using Rocket Boomers to Install Rockbolts Connectable Swellex Rockbolt Corrosion in Mining and Tunnelling Grouting for Support in Tunnels Rock Mass Stability with Swellex Secoroc Uppercut – New Tapered Equipment Getting the Drift with Magnum SR Rock Mechanics and Rock Reinforcement Swellex in Shear Stress Using ROC Drillrigs to Install SDA 3-D Imaging for Rock Support Design Introducing Swellex Hybrid

Case Studies 63 69 73 75 77 81 87 91 97

Swellex in Mining: project reports from Canada, Portugal, Turkey and Peru. Removing Bottlenecks in Austria: upgrading the European highway system in Central Europe. Extreme Temperatures: rock reinforcement in permafrost in Northern Quebec and volcanic strata in Hokkaido. Coated Swellex at Kvarntorp: longlife installation of rockbolts in a corrosive environment. Nuclear Quality Assurance: long-term tunnel support for the Exploratory Studies Facility at Yucca Mountain, US. Versatility in Tunnelling: project reports from China, Germany, Madeira, Spain, and Switzerland. Rapid Support Close to the Face: reporting use of Swellex at three important Italian TBM tunnelling sites. Large Hydroelectric Projects: widely differing demands at sites in Austria, Bhutan, India, Philippines and Portugal. Top Combinations in Japan: reliable support in sedimentary and volcanic rock formations in railway and road tunnels.

99 104 109 113 115 119 124 127 129 131 135

Front Stabilization Using MAI Rock Anchors: pre-reinforcement as a means of ground control in Germany, Italy and Taiwan. Boltec at Kemi Mine: integrated process control demands reliable and consistent mechanized rockbolting. Overcoming Squeezing Ground at Mitholz: supporting deformed strata while fresh support is installed. Mechanized Bolting at Zinkgruvan: better rock reinforcement improves production and safety. Seismic Tunnelling at Bolu: crucial motorway tunnels recover from earthquake using Self Drilling Anchors. SDA in the Baltic States: novel uses for grouted SDA as micropiles to support ancient buildings. Increasing Land Use: SDA applied to subsoil stabilization prior to housebuilding in UK. Soil Nailing UK Transport Routes: securing major road and rail infrastructure using SDA. Portal Support Using Swellex: stabilization of entrances to Porte tunnel in Italy. Driving From Budapest to Nürnberg: difficult tunnels using advanced rock reinforcement techniques. Systematic Grouting at Oslo Subway: Craelius Unigrout provides the perfect solution for water ingress.

Product Specifications 139 144 145 148 149 150 152 164 166 172 174 175 178 180 188 189 190 204

Swellex Manganese Line Plasticoated Swellex Swellex Premium Line Swellex Hybrid Swellex Face Plates & Washers Swellex Pumps MAI SDA Tophammer Crawlers Boltec Rigs Rocket Boomer Drillrigs Hydraulic MAI Bolt Support Hydraulic Rock Drills Hydraulic Feeds Symmetrix Overburden Casing System Unigrout Grout Plant Pusherleg Drills Secoroc Threaded Equipment Secoroc Tapered Equipment

Front cover: Different applications involving rock reinforcement. Atlas Copco reserves the right to alter its specifications at any time. For latest updates contact our local Customer Centers or refer to www.rockreinforcement.com

Produced by tunnelbuilder ltd for Atlas Copco Rock Drills AB, SE-701 91 Orebro, Sweden, tel +46 19 670-7000, fax -7393. Publisher Ulf Linder [email protected] Editor Mike Smith [email protected] Picture Editor Jan Hallgren [email protected] Contributors Anders Arvidsson, Claes Hillblom, Federico Scolari, Francois Charette, Gunnar Nord, Hans Fernberg, Juha Hyvaoja, Jukka Ahonen, Lorne Herron, Mario Bureau, Mark Bernthaler, Olle Karlsson, Per-Olof Einarsson, Sara Sjödin, Sten-Ake Peterson, all [email protected]. Adriana Potts, [email protected]. Maurice Jones, maurice@tunnelbuilder. com. Wulf Schubert, Markus Potsch, Andreas Gaich, all [email protected]. Designed and typeset by Sheldon Mann, Belvedere, Kent, UK Printed by db grafiska, Örebro, Sweden

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Copies of all reference editions are available in CD-ROM format from the publisher, address above. Reproduction of individual

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ngoing development of faster, safer and more exotic tunnelling techniques places a constant pressure on manufacturers to provide more efficient rock support solutions which will help the shortening cycle time. The use of versatile drilling jumbos for mechanized installation of a variety of rock support systems is part of the leading practice used in modern tunnelling. As ground conditions get more and more demanding, emphasis is placed on flexible and intelligent support systems in which rock and soil reinforcement is expected to contribute to the productivity and safety of the operation. The trend has been to provide rock support/reinforcement systems that are easy to install, assure efficiency and provide safety, both during and after excavation. For the last 25 years, Atlas Copco has been offering the Swellex concept as a unique, safe and reliable system of rock support. As the market leader in underground rock excavation technology, Atlas Copco has also been developing safer and more efficient rock reinforcement products such as the Manganese Line rock bolts, which are manufactured from a special type of steel. Another development is the Swellex Premium Line of rock bolts, for use where high yield load and stiffness are expected from the reinforcement system. The recent acquisitions of MAI and Rotex have introduced a whole new range of products, which are now being developed for mechanized installation by both surface and underground drillrigs, creating fresh applications in rock and soil reinforcement. Atlas Copco’s Rock Reinforcement Competence Centre at Feistritz/Drau, Austria brings together the skills necessary for the development of superior rock reinforcement products to serve the tunnelling, mining and construction industries worldwide. In 2005, the centre became a part of Atlas Copco Craelius, which is active in ground engineering with Symmetrix and ODEX overburden casing drilling systems, and Unigrout and Logac grouting equipment, and produces multipurpose drilling rigs such as the Mustang. The combined product portfolio includes Swellex and MAI, bringing together all elements of the Atlas Copco rock and soil reinforcement strategy. As a result, market-driven product development at this new facility is already setting the scene for another quarter-century of development in rock reinforcement and ground engineering.

Federico Scolari Vice President Marketing Atlas Copco Craelius [email protected]

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Innovative Solutions for Rock and Soil Reinforcement Twenty Five Years On Over the past 25 years, Atlas Copco has developed a constant stream of products that have provided innovative solutions to a multitude of rock support and reinforcement tasks, and solved many difficult challenges for miners and drilling contractors around the globe. Further developments are on the way with the recent inauguration of a dedicated competence and R&D centre for rock reinforcement in Feistritz/Drau, Austria. Located at the headquarters of Atlas Copco MAI, the centre is dedicated to developing cutting-edge products for rock reinforcement and ground engineering applications.

Leading the Way When Atlas Copco applied for patents for the Swellex rock bolt in 1979, it was a significant milestone in rock reinforcement technology. This inflatable bolt was extremely easy and quick to install in a 38 mm hole, and provided immediate support. The advantages proved to be so effective that over the next decade several million Swellex bolts were used in demanding ground conditions worldwide. In the years that followed, this success led to the development of several new versions including: • Coated Swellex with rust protection to withstand corrosive environments • Super Swellex for larger hole diameters and a 20-tonne load-bearing capacity • Connectable Swellex for tunnels where the length of the bolt required is more than the height of the tunnel • Swellex Hanger for suspending such facilities as conveyor belts and working platforms ROCK & SOIL REINFORCEMENT

Official opening of the new Atlas Copco rock and soil reinforcement competence centre at Feistritz/Drau, Austria.

Specialized Rigs

launched the Boltec 500, a new rig for fully mechanized rock bolting, primarily to increase productivity and to improve safety when installing the bolts. Safety is an especially important consideration on sites with poor rock conditions. However, the extreme conditions of rock bolting, in which water and rock

At the same time as applying for patents for Swellex, Atlas Copco

Atlas Copco Boltec LC is a highly productive machine developed specifically for rock bolting.

• Swellex Manganese for increased tensile strength and higher elongation capacity • Swellex Premium Line for improved yield characteristics and tensile strength with slightly less elongation.

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stabilization, and in ground engineering for foundation reinforcement. Atlas Copco MAI SDA are now commonly used with modified Boomer drill rigs. In this case, the drill rod and bit are replaced by an MAI adapter, coupling, anchor rod and a sacrificial drill bit.

Competence Centre

Innovative two boom cable bolting rig drills with one boom while feeding and grouting cable with the other.

cuttings pour down along the drill string and onto the rock drill, feed and moving components, had a negative effect on the service life of these rigs. Their performance was affected even more when cement-grouted bolts were used, due to cement spilling out of the hole onto the bolting unit. In response to these challenges, Atlas Copco continued to develop further generations of more rugged and reliable bolting rigs that had fewer moving parts. The current fourth generation rigs are capable of impressive performances. For example, the Boltec LC working in a Finnish mine recently installed more than 120 Swellex Manganese bolts in a single 8-hour shift. Boomer face drilling rigs also began to be used for tunnelling in poor ground, drilling holes for rock bolts as well as for the installation of pipe roofing systems and self-drilling anchors.

this technology, continually setting new standards and breaking new ground. In 2002, the company added self drilling anchors (SDAs) to its ever widening product range, through the acquisition of SDA specialist MAI Ankertechnik of Austria. These fully-threaded anchors, fitted with sacrificial drill bits, are designed for exceptionally poor ground conditions where holes collapse and conventional bolts cannot be used. In addition, they are used in combination with crawler drillrigs for surface applications, such as soil nailing in slope

The recent opening of the dedicated competence centre at Feistritz/Drau, Austria heralds a new era for the development of superior rock reinforcement products to serve tunnelling, mining and construction industries worldwide. A considerable amount of marketdriven product development will now be possible, and customers around the world can expect to see many new and interesting products in this area coming from Atlas Copco in the years ahead. The scene is now set for another quarter-century of development in rock reinforcement and ground engineering. On the following pages, Atlas Copco presents some technical papers, case studies and product specifications to demonstrate this technology in action.

by Federico Scolari Twenty five years of innovative solutions to rock reinforcement problems.

Swellex Still Supreme As the Swellex patents have begun to expire, other producers have made repeated attempts to imitate the design and features of the Swellex bolts, but none have managed to achieve the same quality. Swellex remains supreme, and Atlas Copco remains firmly at the forefront of 4

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Investing in Rock Reinforcement Safety and Economy Time was, in tunnelling and mining, that rock reinforcement was considered a burden, a cost, and a necessary pain. The aim seemed to be to get around the support work in the easiest and cheapest way possible, and concentrate all efforts on excavating the greatest amount of rock, in the shortest time. As the awareness of the consequences of poor rock reinforcement becomes more widespread amongst clients, engineers, miners and contractors around the world, a sounder attitude to this work is emerging. There is now a wish to achieve the required demands on quality, to carry out the support and rock reinforcement in the right order, to properly monitor what has been carried out, and to evaluate the results of the rock reinforcement effort. As contractors and miners have a reputation for looking after their money, new ideas are born on how to carry out the support and reinforcement work in cost efficient ways, and they are often presented as alternatives in their quotations on underground construction projects. In mining, there is continuous ongoing evaluation aimed at optimization of the excavation reinforcement method.

Practical Solutions At Atlas Copco, as a supplier of rock drilling equipment as well as rock reinforcement tools and material, there is an ongoing drive to create new or improved solutions to rock reinforcement problems. This topic is generally broached at an early stage of a project by the contractors, and is brought up constantly by the mining industry. As a result, Atlas Copco is right at the core of practical solutions for rock reinforcement, and this has contributed to our approach. ROCK & SOIL REINFORCEMENT

The latest Atlas Copco Boltec offers a new dimension in rockbolting safety.

The Atlas Copco focus is on total economy, by fast installation of rock support, adequately proven performance of reinforcement, and a technology that has the capacity to meet modern quality demands. In this presentation of the Atlas Copco approach, we discuss the cost implications of the time taken for the round in tunnel excavation, the quality of the Atlas Copco rock reinforcement programme, and working environment and safety aspects.

Improving Performance Going back 20 years or so, and looking into the time needed to excavate a round and how this has developed, will indicate the direction in which tunnelling technology is going. The round cycle is just as real today as it was then. By doubling the effort, the time taken will reduce by 50%.

In a linear situation, for instance, if it takes 100 days for one man to dig a defined dyke, 100 men can do it in one day. In tunnelling, life is not that easy. There may be only one face to work at, and there is usually little space for increased efforts at that face. The only remaining option for the tunnellers is to improve mechanization. The leading process has been drilling at the face. Since the introduction of the original Swedish Method, the drilling performance has improved dramatically. The introduction of heavy pneumatic drifters mounted on articulated booms, followed by three generations of hydraulic drill rigs, has further multiplied productivity. If we consider a tunnel with 80 sq m cross-section being driven in fractured limestone with clays strata, through a couple of major faults, and with 350 m overburden and significant water inflow, the drilling phase has decreased from 40% of the total 5

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will be €500/h saved. Consequently, there is a good incentive for looking for cost saving measures, and rock reinforcement certainly is an area of interest. Atlas Copco has taken this problem seriously. Our approach is to provide machines, rockbolts and know-how to add value to your rock reinforcement. We hope that the articles in this brochure can explain how.

Investing in Rock Reinforcement

Figure 1. Development of face excavation over the last 25 years, showing the changes in time taken for various components of the round.

drilling time 20 years ago, to just 20% today. Figure 1 illustrates the development of drilling and ancillary face operations over 25 years. Not all the different phases in the cycle have the same development. Shotcreting shows a positive trend on time reduction, while mucking has a less noticeable development. These figures would improve for a smaller cross section. Scaling shows a large increase in time, since heavy hydraulic breakers now play an important role in improving the pull of the blasted round by cleaning off the face, as well as trimming the profile of roof and sides to make safe. If we consider traditional, fully grouted rockbolts, installed with a jumbo or with an automatic bolting rig, the increase in productivity does not keep pace with the drilling. In our reference tunnel we can register a poor saving of 10% in total time consumption. Rock reinforcement, and in particular, rockbolting, is a bottleneck in the excavation cycle, and this has to be tackled in order to boost productivity.

with all resources mobilized and the staff taking home their salaries, the cost will be at least half of the forecast cost. Conversely, if the work is carried out in half of the set time, the reduction in cost will be at least 25%. Assume a tunnel of 1.2 km in length, with a cross-section of 70 sq m, will be excavated over a time period of one year. This is an average advance of 100 m/month, at an estimated cost of €5,000/m or €6 million in total. The time related cost will then be at least €3 million, or €2,500/m. If a reduction in construction time of one month can be achieved, it results in a reduction of the cost by €250,000. Further, assuming that the working time is 500 hours/month, then the cost saving

The Atlas Copco commitment is towards a safer and more ergonomic working environment. This commitment is translated into ergonomic machines and reliable rockbolts. There are no shortcuts in this process. Swellex offers immediate support, with full column contact, and pumps check the inflation pressure of the bolts. Self Drilling Anchors (SDA) are replacing manual installation of rockbolts in collapsing holes, where the manual job is more difficult. Boltec offers a new dimension in rockbolting safety, while Cabletec does the same for cable bolting. Assuming that you have done everything to optimize your face drilling, and that your detonators and explosives are the best available. You have a modern ventilation system, the most powerful mucking equipment, and the most efficient shotcrete robot. And you still stay with the most conventional rockbolting system? Then it’s time to invest in rock reinforcement.

by Gunnar Nord

Rocket Boomer L1 C-DH drilling rockbolt holes at Auersmacher in Germany.

Time is Money In tunnelling the time related cost is most likely in the range of 50- 60% of the total cost. This means that, if no work is carried out during the set construction time, 6

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Controllable Rock Reinforcement Helping Rock to Support Itself Modern computer-based geotechnical monitoring techniques indicate that the greatest relaxation or movement of the rock mass occurs immediately following excavation. They confirm that, after a certain period, the rock will establish a new equilibrium based on its own inherent self-supporting capacity. The best quality rock will remain self-supporting for extensive periods of time without the need for extra support. As the rock quality declines, support requirements increase proportionally. The poorer the quality of the rock, the greater the degree of support required, and it becomes increasingly crucial to install reinforcement as quickly and as close to the face as possible after excavation. Engineers involved in the design of rock reinforcement systems must satisfy ever increasing demands to optimize the design to gain maximum safety and economy. The primary objective in the design of the support system is to assist the rock mass to support itself. Accordingly, quality and time are the two main parameters which must be taken into account when determining the type of rockbolt to be used for rock reinforcement, in both mining and construction applications.

Controllability Means Safety

Sequence of installation of a Swellex bolt.

functional. The basic underlying factors are: the inherent sensitivity of resin to heat, age and improper storage; parameters during installation; hole annulus; cartridge damage during insertion; injection nozzle alignment; presence of cracks and flowing water; and levels of operator skill and care. This is a highly unsatisfactory result in terms of worksite safety, and is equally unfavourable in terms of economy. Split-set type bolts may be quick to install, but their anchorage capacity is too low to keep stress concentration at distance from the rock face. By contrast, the Swellex concept entails that the rock is secured by

immediate and full support action from the Swellex bolts. The moment the Swellex bolt is expanded in the hole, it interacts with the rock to maintain its integrity. The quality of the bolt installation is automatically confirmed when the pump stops, and is independent of rock mass conditions or operator experience. Controllability means safety. Control brings peace of mind at every step: 1) Swellex bolts are manufactured following a very strict quality control procedure using specific steels for which origin and composition are known and controlled.

High pressure water expands the Swellex bolt into contact with the strata.

Traditionally, the use of rockbolts has been limited to reinforcing reasonably solid rock. Poorly consolidated and friable rock conditions have required the use of expensive external support. Independent surveys reveal that as many as 50% of cement- and resingrouted rockbolts are so poorly installed that they are virtually non-

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arch or beam. Reinforcement is unaffected by the presence of water, or joints in the rock mass. Swellex rockbolts, and the quality assured installation procedure, permit rock reinforcement where expensive external support is normally required.

Immediate Support

Plasticoated Swellex with cap and without cap.

All the manufacturing parameters are filed and linked to a number on the Swellex bolt bushing for traceability. 2) Installation of Swellex bolts is controlled by sturdy Atlas Copco pumps to assure a perfect installation. The new patented HC1 pump, once started, will only stop when the set pressure is reached, independently of the operator. 3) Pull-tests can be performed at any time on Swellex bolts. Whether they were installed a year ago in a corrosive environment, or 10 years ago in a dry area, it is possible to control their load bearing and yielding capacity. Expertise has also been developed for examining the bolts with a fibre optic camera to control internal corrosion or shearing. The Swellex concept is designed to optimize the effectiveness of each bolt, so the bolting operation matches the required safety levels as planned by the engineers. Alternatively, compared to other rock support, the same bolting effort using the Swellex system can result in increased safety, since each installed Swellex bolt provides full support. Swellex rockbolts have been used successfully to complete many tunnels in difficult rock conditions while, at the same time, greatly reducing support costs. 8

Swellex rockbolts reinforce and improve the condition of the interfacing rock, increasing its load-bearing capacity. Depending on the rock mass strength, the pressure exerted during installation may compact the rock surrounding the borehole, increasing the friction along the bolt, and/or deform its profile to match the irregularities of the rock, providing a combination of strong mechanical interlocking and high friction. The resulting high anchorage capacity makes Swellex bolts an integral part of the supporting

Modern drilling and excavation equipment used in civil engineering and mining applications has led to major increases in efficiency and productivity. In fact, development has been so rapid that conventional rockbolting methods frequently act as production bottlenecks. Developments in the speed and ease with which rock reinforcement can be applied to improve equipment utilization, limit machine downtime, and increase productivity, while simultaneously complying with safety requirements, is of interest to all those involved in tunnelling and mining. The Swellex concept has kept pace with these advances, with a single operator installing 50 to 100 bolts/shift. Timing of the rock reinforcement measures is of particular importance in NATM, the New Austrian Tunnelling Method. In brief, NATM can be expressed as a sequence of activities for tunnel development: drilling and

Mn24H hanger rockbolts for suspending utilities while reinforcing the rock.

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blasting; mucking and scaling; and immediate initial rock mass support by systematic rockbolting and shotcreting. The initial support system restricts ground movements after excavation, thereby maintaining the inherent strength of the rock mass. This is the essential idea behind NATM. The permanent lining is installed when the rock has reached a state of equilibrium, and deformation has ceased. Swellex rockbolts provide immediate support, as well as the ability to accommodate large ground movements at maximum load-bearing capacity. Shear tests performed by several international institutes have shown that, depending on rock compressive strength, Swellex bolts can accommodate up to 90-100% of their tensile strength under shear loading, an exceptionally high figure. Joint shear displacement at bolt failure can be up to 35 mm/56 mm at a 90 degree angle between the bolt and the surface of the joint, showing that Swellex bolts accommodate the same amount of shear displacement as the diameter of the drill hole, and even more in softer rock.

The Right Protection When it comes to choosing the right product for longevity, or for use in a corrosive environment, it is advisable to proceed with caution. There are many products that offer what appears to be lifetime protection. Unfortunately, in reality, the rock mass properties such as water, joints, rock movement, may be unknown, and the quality of rockbolt installation may be unquantifiable. Conventional types of rockbolts made from carbon steel are susceptible to corrosion. As only 50-70% of resin coated and grouted bolts are properly installed, they do not represent a reliable solution against corrosion. Also, there is extra delay and cost associated with these bolts, compared to the Swellex solution. To help choose the right alternative, Atlas Copco is using reputable corrosion institutes around the world to assess the corrosion potential of ROCK & SOIL REINFORCEMENT

Hybrid bolt for long anchorage in rock.

ground water around the rockbolt and inflation water within the rockbolt. It has been established that, for medium term corrosion protection, the bitumen coating is best. However, plasticoated Swellex offers longterm corrosion protection, independently of the rock mass parameter. If shotcrete or sealant are used, the threat from atmospheric corrosion diminishes. In the case of Swellex, it will seal and protect the inside of the bolt, leaving a reduced corrosion potential to the external side only. If there is no shotcrete or sealant applied after bolt installation, caps can be used to seal the bolt internally. A real level of safety is achieved with Swellex, as the corrosion is assessed, and the bolt can be controlled using pull test or internal visual inspection over time.

Total System Approach The cost and time involved in rock reinforcement compels project engineers to evaluate a total system approach. The cost of the rockbolt itself, or such properties as tensile strength, are seldom of primary interest. The decisive factors are the resulting safety, the total cost, and the time required to fulfil the mission. A productivity study comparing Swellex to other bolts in a gold mine

in Canada has proved that Swellex boosted metres of advance by 10% and reduced bolting costs by 10%. As more bolts were installed per working shift, fixed costs for manpower and rigs were diluted, resulting in increased metres of advance/shift with improved safety. For similar reasons, Swellex has became a standard in most European countries and in Japan. To summarize, when the Swellex bolt is installed in heavily fissured rock, the radial stresses enhance the contact forces between blocks of rock surrounding the bolt, leading to an increase in rock mass strength. In soils, Swellex bolts provide consolidation immediately around the bolt, leading to an increase in the strength of the material, and improved anchoring capacity of the rockbolt. In hard rock, 0.5 m of anchored Swellex rockbolt gives a pullout resistance equal to the breaking load of the bolt. A strong anchorage capacity will help to distribute the stress around the excavation and avoid stress concentration close to the surface that can lead to rock falls or strain burst. There are Swellex rockbolts for almost any environment and purpose. Swellex Mn12 and Pm12 are perfect for regular daily support in mining and tunnelling. When high loading capacity is needed, Swellex Mn24 or Pm24 is the answer. Swellex Mn16 and Pm16 are a cost-effective solution when 43-52 mm drilling is preferred. In highly corrosive conditions, or where there are demands for long life, Coated or Plasticoated Swellex may be the choice. In situations where very long bolts are required, or in confined space, Mn24E Extendable Swellex offers fast installation of up to 12 mlong bolts. Recent years have seen the development of the Mn24H, a type of Swellex that is part of the rock support and is also used to hang heavy loads without inducing unfavourable stress in the bolt’s head bushing. Atlas Copco is also proud of its latest patented hybrid system of rock reinforcement, see article in this issue.

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Swellex Manganese Offers Improved Work Index Tough Newcomer Atlas Copco’s Swellex rockbolts have a long and successful history based on two simple advantages for the customer: safety and productivity. Swellex rockbolts are watertight, doublefolded, high-quality steel tubes, which are expanded by a highpressure water pump through a pre-drilled hole. The expansion of the tube generates both contact friction and mechanical interlock between the steel and surrounding rock, giving immediate and full-column rock reinforcement in a simple and rapid way. The latest range of frictional bolts, marketed as Swellex Manganese, will dramatically increase performance, thanks to a new steel composition and an innovative heat treatment.

New Tool Atlas Copco research and development has engineered a new generation of Swellex bolt, which will better suit the rock mechanical requirements. At the same time, it was decided to further increase the productivity, performance and reliability of Swellex pumps. By these means, a quantum leap forward in safety and performance has been achieved. Loading capacity normally defines a class of rock bolt. For example, Standard Swellex is a 100 kN bolt, while Super Swellex is in the 190 kN category. But other parameters can influence the final performance of a rockbolt, and especially its contribution to safety. Experience in mining and tunnelling operations has shown that elongation is a very important parameter in judging the performance of a bolt. In deep mines, strain concentration areas, uneven load, progressive ROCK & SOIL REINFORCEMENT

Wi

Wi

Figure 1. The excellent performance of the Super Swellex rockbolt is further improved by Swellex Mn24, the corresponding bolt in the new Manganese Line.

deformation and squeezing ground are all cases in which a bolt with a superior capacity to follow the rock deformation can play an important role in balancing and re-adjusting the strain field towards stability. But elongation without tensile strength is simply out of the question. Atlas Copco needed a new tool to measure the total performance of rockbolts, and a new parameter capable of combining capacity and elongation. As the deformation is expressed in percent (%) in the classical load deformation graph Atlas Copco is introducing the Work Index (Wi). The Work Index (Wi) as real work is defined by the integral of load in function of the deformation also represented by the area beneath the curve in Figure 1. The Work Index (Wi) gives a truthful picture of the total energy absorbed by the bolt before breaking down, or losing its function.

Search For Excellence The Swellex range is based on several hole sizes. Standard Swellex is used in combination with holes from 32 mm to 39 mm-diameter, while both Super and Midi Swellex work in the 43 mm to 52 mm range. A possible solution to increase the Work Index was to increase the geometrical feature of the bolts. Considering the Swellex position as an established worldwide commercial success, it did not make sense to modify its well-accepted and fit-toapplication dimensions. It was more logical to work on material properties and production methods. The steel used in Swellex is already a special type, with few impurities. Well-established co-operation with a leading steel supplier and with a pipe mill allowed a tailored technical specification to be developed for materials, 11

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Figure 2. After a series of experiments, a heattreated Manganese steel was chosen. This table shows the results of the design efforts with respect to tensile tests of the profile after expansion to simulate real conditions.

Summary of Swellex® user benefits ●

Swellex provides costeffective rock reinforcement in most rock types and conditions.

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Swellex installation procedure ensures that every bolt installed will provide optimum reinforcement.

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Swellex rock bolts are quickly installed, and very little training is required to use the equipment.

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Swellex rock bolts provide full column interlock with the surrounding rock, without the need for mechanical locking devices or grouting agents.

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Swellex requires no environmentally harmful chemical grouts to anchor the bolt in the rock.

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The quick and easy installation, and the assurance that every bolt provides immediate full load-bearing capacity, makes Swellex the most cost-effective rock reinforcement.

and a series of alloys and high tensile steels were considered. Only a limited number of options can handle the severe requirement of Swellex rockbolts with respect to radial deformation during expansion, and weldability to assure perfect watertight contacts at the bushings. It was decided to use a better quality steel, with a higher manganese content. Produced in a cold forming mill, the steel reaches a very high tensile strength and high loading capacity, but unsatisfactory elongation. A postproduction heat treatment is then used to produce the extraordinary elongation properties needed for the Swellex profile.

Improved Behaviour Figure 1 compares typical load/ deformation curves for Super Swellex and the new Swellex Mn24. In particular, the regular Swellex steel profile shows a classical behaviour for carbon steel. Beyond the yielding point (200 kN), the profile accepts a large amount of deformation, but with slightly lower strength. When a 20% elongation is reached, the profile breaks down. The new, high-strength and fully annealed Manganese Line now offers

a higher loading capacity and, at the same time, enhanced elongation. Figure 1 shows that, beyond yielding point, the manganese steel increases the load capacity due to the hardening process. The curve continues to point upwards until a 10% elongation is achieved, then a long horizontal segment goes above the 30% level before the profile breaks up. This extraordinary behaviour gives the capacity to absorb a substantially higher quantity of energy, as indicated in the 80% increase in the Work Index shown in Figure 2.

Total Reliability The heat treatment used during the production of the new Swellex Manganese Line further improves repeatability of the performance obtainable by the bolts. A large number of pull tests, representative for millions of rockbolts, show very little variation in the results. As a result, engineers, miners, rockmechanics and consultants can rely on safe and quality controlled rockbolts, through the entire process from manufacturing to installation.

by Federico Scolari Work Index for various types of bolts.

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Manganese and Premium Lines Continuous Improvement Atlas Copco has, over the years, improved considerably the Swellex system. Rock engineers are extremely conscious that the behaviour and efficiency of rock bolts can be dictated by the properties of the steel from which they are made. Accordingly, rock bolts are no longer judged simply by their maximum tensile strength. The rock mass stresses surrounding underground excavations have to be tamed using energy rather than strength. Sometimes, it is better to bend with the stress, while in other instances stiffness is preferable. It all depends on the type of rock, excavation size, geology, stress field evolution, seismicity, corrosion and longevity required. Atlas Copco, which introduced the Manganese Mn Line of Swellex rock bolts a couple of years ago, has recently launched the Premium Pm Line.

Competence Centre The Rock Reinforcement Competence Centre team at Atlas Copco understands the requirements of different rock reinforcement situations, and has

Yield Load kN (Rp02) Min. Breaking Load kN Min. Elongation % Working index

Mn12 75 100 20 2000

Pm12 100 120 15 1800

Yield Load kN (Rp02) Min. Breaking Load kN Min. Elongation % Working index

Mn16 105 140 20 2800

Pm16 130 160 15 2400

Yield Load kN (Rp02) Min. Breaking Load kN Min. Elongation % Working index

Mn24 150 200 20 4000

Pm24 200 240 15 3600

Comparison tables for Mn and Pm bolts.

striven over the years to develop support systems using the best available steel for each application. Once the anchorage mechanism is understood, the best way to predict how the rock support will interact with the rock mass is to look at the steel load-deformation graph. It is preferable to assess graphs from manufactured product instead of the virgin steel, as the manufacturing process will modify the property of the steel and the way the support will behave under load.

Mn Line Mn Line bolts are made out of high strength steel, profiled, welded and heat-treated to survive extensive deformation at maximum strength for high-energy consumption before reaching failure. Furthermore, the plastic zone is characterized by a continuous progression of the load that allows, when the bolt is installed in rock, a progressive debonding. As the diameter of the loaded section reduces Typical load/strain graphs for Pm24 and Mn24 bolts.

300

Pm24 Mn24

250 200 150

LOAD(kN)

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20

25

30

35

STRAIN (%)

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under plastic deformation, a succession of new sections are progressively released to work and stretch, providing extra energy absorbency and avoiding rapid failure. Mn Line bolts are therefore best suited to an environment where rock mass stress is high and unstable, requiring good energy absorbency capacity. Typical applications for the Mn Line are where deformation/stress of the rock mass is unstable in time. These situations occur in mining stopes, deep mining, mining in a high stress environment caused by poor geology or faulting, and mining in zones where movement is expected in the walls or roof resulting in stress increase with time.

Premium Line The Pm Line is also made of high strength steel but having different properties than the steel used for the Mn Line. No heat treatment is given to the Pm bolts, resulting in a very stiff behaviour at high load, because the yielding strength is very close to the maximum tensile strength. Pm Line bolts are used where maximum control of the rock mass convergence is targeted, and a high yielding load capacity (Rp02) and stiffness are required, as in civil tunnelling projects.

Checking nut and plate on Swellex Premium bolt.

Typical applications for the Pm Line are where deformation/stress of the rock mass is stable in time and high stiffness is required. These situations occur in tunneling, beam consolidation of strata in mining, mining where the rock mass stress and movement are low or stable in time, and the yielding load will never be reached, and mining and tunnelling in soft rock.

Atlas Copco is continuously investing in research and development to offer the market the best rock reinforcement products with safety and productivity in mind. The right steel for the application adds safety and productivity!

by Mario Bureau

Choice of Reinforcement Type Conditions

Soft Rock and low to medium stresses Soft Rock and high Stresses Weathered hard rock or laminated/ schistose rock and high stresses Hard Rock and low to medium stresses Hard Rock and high Stresses

14

Properties of reinforcement

Preferred Reinforcement/ Support Types

High Stiffness

Swellex Pm Line

Yielding and high anchorage

Swellex Mn Line + Connectable and Hybrid

High Stiffness

Swellex Pm Line + Swellex Hybrid cemented

Yielding and retention capacity

Swellex Mn Line + Swellex Hybrid non-cemented for rock burst (seismicity & strain bursting)

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Hollow-Core Self Drilling Anchoring Systems Support Without Casing The Atlas Copco MAI Self Drilling Anchoring System is a fully threaded steel bar which can be drilled and grouted into loose or collapsing soils without the use of a casing. The bar, or SDA, features a hollow bore for flushing, or simultaneous drilling and grouting, and has a left-hand rope thread for connection to standard drill tooling. The Atlas Copco MAI SDA can be installed in a variety of different soils and ground conditions ranging from sand and gravel to inconsistent fill, boulders, rubble and weathered rock, as well as through footings and base slabs. Applications associated with underground works include: radial anchoring for stabilization of tunnel circumference during NATM-style excavation; as forepoles, spiles or umbrella for advance protection of the excavation; as root piles for reaction load of steel support arches; and for slope stabilization of the tunnel portal.

MAI SDA Functional Parts The system elements of the Atlas Copco MAI Self Drilling Anchor (SDA) are as follows: The Atlas Copco MAI bar, which is manufactured from API standard heavy walling steel tubing, cold rolled to form a standard ISO rope thread profile. The rolling process refines the grain structure of the steel, increasing the yield strength, and producing a durable drill rod suitable for a range of applications. The standard rope thread of the Atlas Copco MAI bar produces an excellent bond between the bar and grout, as well as enabling connection to all Atlas Copco Boomer and surface drill rigs, and use with a wide range of drill steel accessories. ROCK & SOIL REINFORCEMENT

The MAI bar is produced in 12 m lengths and then cut to size depending on customer requirements. Standard delivery lengths are 1 m, 2 m, 3 m, 4 m and 6 m. Recommended maximum bar lengths depend on diameter and can be up to 6.0 m. Additional lengths up to 12.0 m are available on request. The Atlas Copco MAI coupler, which features a patented design that enables direct end-to-end bearing between each bar, reducing energy loss and ensuring maximum percussive energy at the drill bit. The coupler design has a thread arrangement in which the top half of the thread is rotated against that of the lower half, providing a centre stop for each bar. All couplers exceed the ultimate strength of the bar by 20%. To enable the correct seating of each bar within the coupler, all bars have a precision cut at right angles to enable end to end bearing. A quarter turn back of the coupler on the lower bar will ensure optimum seating of the upper bar within the coupler. The Atlas Copco MAI hexagonal nut, which is machined with chamfered edges on both ends from high precision steel, and tempered to meet any stringent demands of the anchor specifications and the daily operations of underground works. All nuts exceed the ultimate strength of the bar by 20%. The Atlas Copco MAI bearing plate, which is a formed steel plate with a centre hole, allowing articulation of seven degrees in all directions. All functional parts are constantly tested, in line with the company’s rigorous quality assurance policy. The sacrificial Atlas Copco MAI drill bit is the most crucial part of the anchor system, and is responsible for the productivity of the installation. Atlas Copco MAI maintains a large range of drill bits to suit the changing demands of geology encountered on different projects. In order to improve on performance and cost efficiency,

MAI SDA arrangement, showing threaded bar, coupler, nut, plate and bit.

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Installation sequence of MAI SDA.

data is collected from projects around the world, and incorporated into the design with the aim to improve penetration rate and bit quality, and to reduce manufacturing costs.

Overall Advantages of MAI SDA Advantages of the Atlas Copco MAI SDA system are that it is particularly suitable for very difficult and unstable ground conditions, such as broken, fissured and fractured rock formations, or unconsolidated sands and gravels. Re-drilling time due to collapsing boreholes is avoided, and speed of installation is high, with no primary drilling required. The drilling, placing and grouting of the anchor is performed in one single operation, reducing the drill labour compared to cased boreholes. Since conventional rotary-percussion drilling equipment is used, the method of installation is very similar for all ground conditions, and the bolts can be installed in all directions, including upwards. There is an option to use simultaneous drilling and grouting techniques during installation, to consolidate any surrounding loose ground. The anchor bar consists of a full length left hand rope thread, which gives the flexibility to adjust the bar length to the actual requirement. This is especially useful if anchoring has to be performed in a confined workspace.

Method of Installation Self Drilling Anchors are installed with air driven or hydraulic rotary percussion drilling equipment, using a 16

borehole flush medium suitable for the specific ground conditions. There are three types of borehole flush: 1) water flush for long boreholes in dense sand, gravel formation or rock conditions, for a better transportation of large cuttings and cooling of the drill bit; 2) air flush for short boreholes in soft soil, such as chalk and clay, where water spillage is to be avoided; 3) simultaneous drilling and grouting (SDG), for all lengths of boreholes in all unconsolidated soil conditions. Using SDG, the grout stabilizes the borehole during installation, providing a better grout cover along the nail shaft. The grout has good penetration into the surrounding soil, so higher external friction values are reached, and the installation is completed in a single drilling operation, saving time. By utilizing a sacrificial drill bit, the MAI SDA is drilled continuously forward without extraction, until the design depth is reached. To reach a required nail length of 12-15 m, the 3 to 4 m standard rod lengths are easily coupled together. When using the first two flushing media for the drilling operation, the soil/steel interface has to be created by grouting through the hollow stem of the anchor rockbolt. The grout exits through the flush holes of the drill bit, and backfills the annulus around the anchor that has been cut by the larger diameter of the drill bit. For simultaneous operation, the flushing medium is already a grout mix, which has the ability to harden after the installation process is completed.

MAI PUMP The One and Only

by Mark Bernthaler ROCK & SOIL REINFORCEMENT

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Atlas Copco MAI Self Drilling Anchors Productivity and Problem Solving The Atlas Copco MAI SDA is a unique bolting solution for unstable ground conditions such as sand, gravel, silt, and clays, and in soft to medium fractured rock formations. When discussing productivity, only projects facing such ground conditions should be considered. Conventional rockbolts, or soil nails, generally have the disadvantage that, when being installed in poor ground conditions, unproductive time is spent on measures such as: retrieving expensive drill tools from collapsed boreholes; repositioning the drill feed to clean collapsed boreholes; introducing the grout hose to the borehole bottom, and grouting the borehole; and inserting the nail or rockbolt with the assistance of the feed system of the drilling unit. The Atlas Copco MAI SDA system is designed to avoid most such time losses. With an optimized installation method, tailored to the project’s needs, the ultimate aim should be to limit the installation time to the actual drilling time of the borehole.

Atlas Copco MAI SDA Techniques Post installation grouting A number of Atlas Copco MAI SDA bolts are installed in one phase to limit the working time of the drilling equipment and make it available for other drilling operations within the excavation cycle. The grouting is performed as an independent operation from a separate support vehicle. Installation and successive grouting In order to utilize this system, an Integrated Rotary Injection Adapter (Ceminject) is mounted between the ROCK & SOIL REINFORCEMENT

Integrated Rotary Injection Adapter (Ceminject) mounted on a Boomer.

COP hammer and the anchor bar. Drilling is carried out using water or air flushing, but, upon reaching the planned borehole depth, a suitable cement mix is immediately injected. By slow rotation while applying backwards and forwards movement of the SDA, the grout is pushed under pressure from the bottom of the borehole towards the borehole mouth. It mixes in the borehole to provide optimum backfilling of the borehole annulus contact to the soil. The advantage of this system is the reduction of cement consumption in horizontal boreholes. Simultaneous drilling and grouting Similar to the successive grouting method, this system also requires the use of a Integrated Rotary Injection Adapter (Ceminject). However, instead of drilling with air or water flush, a suitable grout mix is introduced. The following advantages are achieved: stabilization of the

borehole and optimum filling of the annulus; improved protection against corrosion; and consolidation of gravel, fissures, fractures or voids surrounding the borehole.

Time Saving Atlas Copco envisages full mechanization of the Atlas Copco MAI SDA to reduce the installation time and increase its productivity. The company is also interested in resolving particular site problems, and in advancing tunnel technology for typical applications of Self Drilling Anchors. These are, in particular: radial nailing of the tunnel circumference; forepoling for cylindrical tunnel advance, using lengths of approximately 4 m with 1 m overlap and face stabilization using lengths up to 15 m, and root piles. Worldwide, underground projects are designed with geological expectations based on information received 17

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Time savings by using MAI SDA System.

from rather limited soil investigations. Furthermore, today’s need to satisfy the design requirements for infrastructure projects mostly doesn’t allow a route selection that follows only good rock conditions. This increasingly demands flexibility by the contractor, who may be forced to adjust at short notice to unpredicted changes in geological conditions. Construction sites today have the option to cater for every eventuality, and to maintain tools at site for every type of ground condition. Prior planning by the site management to maintain sufficient quantities of Atlas Copco MAI SDA available for use can

allow an immediate intervention, reducing time wastage and increasing productivity. The design of the Atlas Copco MAI SDA also favours productivity in terms of storage and handling. Anchor bars with a continuous left hand thread are delivered to site in standard lengths of 2 m, 3 m, 4 m and 6 m, and can be assembled to the specific lengths required. Transport to site, and onward to the working area, is simplified, due to the short lengths of the anchor elements and their accessories.

by Mark Bernthaler

Delivery lengths of Atlas Copco MAI SDA.

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Larger and Deeper Holes With Symmetrix New World of Construction When Atlas Copco acquired the Rotex company of Finland in 2004, it represented a major step forward for contractors in the field of overburden drilling and related technologies. In addition to its well-proven ODEX equipment, Atlas Copco is now able to offer Symmetrix, a unique system that enables drillers to drill deeper and larger holes than ever before.

More Applications The ODEX method of overburden drilling with an eccentric bit is well established amongst drillers, particularly when it comes to shallow, small dimension holes. Now, with the introduction of the Symmetrix system, Atlas Copco has opened the door to an infinite number of applications where casing drilling is the preferred solution for forepoling, micropiling and other types of ground engineering work. Symmetrix enables drillers to go larger and deeper than ever before. Whereas the ODEX method is ideal for drilling holes up to 273 mm in diameter, Symmetrix handles the installation of casings up to 1.2 m in diameter, in holes of 100 m-deep (300 ft) and beyond. This unique capability gives contractors the power to tackle any type of casing advancing work, from micropiling, tunnel forepoling, and foundation piling, to opening ‘ratholes’ for oil and gas wells, as well as horizontal casing drilling. In addition, the Symmetrix system is a perfect complement to Atlas Copco’s extensive range of DTH (Down-The-Hole) equipment. The Secoroc DTH hammers for ROCK & SOIL REINFORCEMENT

overburden drilling, the speciallydesigned Mustang rigs for anchor drilling and micropiling, and the DTH products provided by Atlas Copco Drilling Solutions in the US, provide sufficient combinations to meet most overburden challenges.

Case for Casings There is no doubt that the use of drilled casings in underground construction is becoming increasingly popular worldwide, primarily due to the expansion of building and infrastructure growth in areas that are less than ideal for such development. Pile driving in dense urban conditions can disturb surrounding structures or utilities, and is often difficult to estimate in terms of costs. This is compounded by other problems, such as ground settlement, soil compaction and lateral soil displacement. When using a drill casing, soil, rock and other debris are removed within a protective steel tube and brought to the surface. For foundations, during

Symmetrix RC system used in Turku, Finland.

the concreting process the support is transferred from the temporary drill casing, which is gradually withdrawn, to the concrete that forms the pile shaft. Likewise, the casing may be left in place as additional structural support, or for protection of the pile. For exploration and well drilling, the casing can become the conduit for bringing the debris to the surface. For these reasons, designers and owners turn to drilled casings, and DTH drilling with Symmetrix is often the only method that can drill through all ground conditions, boulders and solid rock.

Symmetrix in Sensitive Conditions The Marina Palace Hotel, a large hotel and congress center located in the old city of Turku on the south western coast of Finland, is going through a main renovation scheme. Part of the project is to enlarge the parking capacity by building an underground parking lot. Ground conditions 19

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ROTARY MOTOR

Principle of the Symmetrix system 1) The casing tube is drilled to the required depth.

COMPRESSOR

CUTTINGS

2) The pilot bit is withdrawn from the casing. 3) The casing is left in the hole as a support for the pile.

CASING PIPE OVERBURDEN

DUAL WALL DRILL PIPE INTERCHANGE

1

2

3

CASING SHOE SYMMETRIX BIT

in Turku are problematic, with mainly post glacier clays at surface overlaying sand layers containing high water pressure. This is followed by till containing very hard boulders typically sitting on steeply inclined non-weathered hard granite or diabase. Completing a deep pile at Marina Palace Hotel, Turku.

20

The old town is built mainly on wooden driven piles. These are being replaced by steel casings drilled all the way to bedrock, for which several underpinning projects are underway on the northern banks of the Aura river. In the Marina Palace Hotel parking garage project, clay and till layers reach 35 m-deep in the northern corner of the site, and the till is 65 m-

deep on the southern riverside. For the garage foundation, steel casings are being drilled 1 m or 2 m into the solid bed rock, which means that longest casings are 67-68 m-long. Drilling work is being carried out by Skanska and their subcontractor, Sotkamon Porakaivo. Casing sizes are from 140 mm to 508 mm, all of which are thick walled to form load bearing members. Most of these casings are in sensitive conditions very close to existing buildings and their foundations, so a unique drilling system is required. Atlas Copco Rotex has developed reverse flushing drill bits in order to control the air flushing in sensitive conditions. Symmetrix RC is designed to give the straightness the consulting engineers require, control of flushing media needed under existing foundations, and high productivity in virtually any ground condition. The Symmetrix RC system specified by the supervising design engineering company for the Marina Palace Hotel job is being used on all four drillrigs. Hard, rubber-like clays are normally expected to be problematic, but subcontractor Sotkamon Porakaivo reports

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the locking mechanism and flushing holes. The system consists of three main components working together as a single unit – a pilot bit with large internal flushing holes and external flushing grooves, a symmetrical ring bit (reamer) with internal bayonet coupling, and a casing shoe for driving the casing. The pilot bit is attached to the ring bit with a bayonet coupling. Together they rotate clockwise and cut a hole sufficiently large to allow the casing shoe to pull down the casing pipe. The ring bit rotates freely on the casing shoe, which is welded to the casing. During drilling, the casing does not rotate. Casings can be added to the string as required. The flushing air is ejected through the holes in the face of the pilot bit, and returns immediately up wide grooves between the pilot bit and ring bit and the annulus between the casing and the drill string. This ensures high flushing velocity with low hole degradation. When the hole is complete, the pilot bit is unlocked from the ring bit with a slight counter-clockwise motion, and withdrawn up through the casing. The casing can then be either left in place or retrieved from the hole.

Future Development

Drilling close to existing structures.

that Symmetrix RC has made drilling very easy and productive, with casings going in very straight and fast all the way through clays, sands, boulders, till, and even into very hard bedrock.

Symmetrix Secret So what makes the Symmetrix casing advancing method so unique? Basically, the secret lies in the patented design of

What it means for the contractor Symmetrix systems come in a large number of versions and sizes to suit a wide range of applications. These include: piling; forepiling and micropiling using both temporary and permanent casing; underpinning with grouted columns; well drilling; and horizontal casing drilling. For the overburden drilling contractor this means: straight holes without risk of deviation; quick setup and high production rates; less torque required in all formations; easy to lock and relock; convenient drilling at any angle; no jamming and lost bits; can be used in all ground conditions and at any angle down to 100 m (300 ft) and beyond; and significant economic savings.

ROCK & SOIL REINFORCEMENT

The technology of casing drilling is constantly developing, and the demand is increasing fast in many different applications. One of the biggest growth areas is in drilling in urban environments, where it is no longer possible to open up the streets for further drilling work without disturbing vital installations. Here, Symmetrix will have a major role to play. Large city subways are typical cases where tunnel roofs have to be pipe-drilled in order to connect one underpass to another. With Symmetrix on board, Atlas Copco is able to provide customers with state-of-the-art casing drilling technology that can meet these challenges, and many more besides.

by Jukka Ahonen Product Manager, Atlas Copco Rotex 21

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Sacrificial Drillbits

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Mechanized Bolting and Screening Utilization is the Key For civil engineering applications such as tunnelling, it is quite common to use the same equipment for all drilling requirements. These days, a single drillrig can accommodate drilling for face blasting, bolt holes, protection umbrellas, and drainage. As there are normally only one or two faces available for work before blasting and mucking, it is difficult to obtain high utilization for specialized equipment such as mechanized bolting rigs. By contrast, in underground mining, especially where a number of working areas are accessible using methods such as room and pillar, high utilization of specialized equipment can be expected.

Specializing for Safety There was a time when underground mining and safety were terms not commonly referred to in the same sentence. However, times have changed, and today safety is given a place of prominence in the operational priorities of the mining industry. Freshly blasted openings leave considerable areas of loose rock, which must be removed to prevent fall-ofground injuries. Improvements in drilling and blasting techniques have helped to significantly reduce the amount of this loose rock. Scaling, which is the most hazardous part of the work cycle, is used to remove the visible loose rock. Subsequent blasting might result in additional rock falls, especially in fractured ground conditions. Screening or shotcreting, as a means of retention of this loose rock, is often used in combination with rockbolting. Screening, which is a time-consuming operation, 24

Mechanized bolting underway using Boltec.

is common practice in Canada and Australia. Since the 1960s and 1970s, considerable effort has been spent on mechanizing underground operational activities, including the rock excavation cycle. Within the drill-blast-muck cycle repeated for each round, the drilling phase has become fully mechanized, with the advent of high productivity hydraulic drill jumbos. Similarly, blasting has become an efficient process, thanks to the development of bulk charging trucks and easily configured detonation systems. After only a short delay to provide for adequate removal of dust and smoke by high capacity ventilation systems, the modern LHD rapidly cleans out the muck pile. These phases of the work cycle have been successfully mechanized, and modern equipment provides a safe operator environment. By contrast, the most hazardous operations, such as scaling, bolting and screening, have only enjoyed limited progress in terms of productivity improvements and degree of mechanization. The development of mechanized scaling and bolting rigs has been slower, mainly due to variations in

safety rules and works procedure in specific rock conditions. To summarize, equipment manufacturers have had difficulty in providing globally accepted solutions. Nevertheless, there is equipment available to meet most of the current demands from miners and tunnellers. However, there is a perception that equipment for full mechanization of rockbolting is expensive, and a largescale consumer of parts and components.

Mechanization Stages Various methods of mechanized bolting are available, and these can be listed under the following three headings.

manual drilling and bolting This method employs light hand held rock drills, scaling bars and bolt installation equipment, and was in widespread use until the advent of hydraulic drilling in the 1970s. Manual methods are still used in small drifts and tunnels, where drilling is performed with handheld pneumatic rock drills. The bolt holes are drilled with the same equipment, or with stopers. Bolts, with or without grouting, are installed manually with impact ROCK & SOIL REINFORCEMENT

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New generation Boltec LC rig installing screen.

wrenches. To facilitate access to high roofs, service trucks or cars, with elevated platforms, are commonly used.

semi-mechanized drilling and bolting The drilling is mechanized, using a hydraulic drill jumbo, followed by manual installation of the bolts by operators working from a platform mounted on the drill rig, or on a separate vehicle. The man-basket, as a working platform, limits both the practical working space and the retreat capability in the event of falling rock. In larger tunnels, the bolt holes are drilled with the face drilling jumbo.

fully mechanized work cycle A special truck, equipped with boom mounted hydraulic breakers, performs the hazardous scaling job, with the ROCK & SOIL REINFORCEMENT

operator remotely located, away from rock falls. Blast holes are drilled in the face using a drill jumbo, and all functions in the rock support process are performed at a safe distance from the rock to be supported. The operator controls everything from a platform or cabin, usually equipped with a protective roof. Where installation of steel mesh is undertaken, some manual jobs may still be required. Mesh is tricky to handle, because of its shape and weight, and this has hampered development of fully automated erection.

Quality of Bolting In 1992, it was reported that independent studies were indicating that as many as 20-40 % of cement and resin grouted bolts in current use were

non-functional. Tunnellers were reporting that they were not installing bolts close to the working face, because they might fall out when blasting the round. Obviously, a large proportion of rockbolts were being installed for psychological reasons, rather than for good face support and a safe working environment. However, by using a mechanized installation procedure, the quality of installation improves. The bolt can be installed directly after the hole has been drilled; the grout can be measured and adjusted to the hole size; and bolt installation can be automated, which is especially important when using resin cartridges, where time and mixing speed are crucial. It can be proved that mechanization and automation of the rockbolting process offers improved quality and safety. While mining companies and equipment manufacturers, especially in Canada, focused their development on improving semi-mechanized roof support, evolution in Europe concentrated on fully automated bolting. During the 1990s, progress accelerated, and today, around 15 % of all bolting in underground mines worldwide is carried out by fully mechanized bolting rigs. However, compared to mechanization of face drilling and production drilling, this level of acceptance is far from impressive, and the industry has been slow to accept the principle. The more obvious positive safety aspects of mechanized rockbolting have been sidelined by considerations relating to the scale of operations and the type of equipment available. Hence the higher acceptance in mining, where several faces are operated simultaneously. For tunnelling applications, where the rate of advance is of prime importance, the economic criteria might be different. Also, as there are more functions incorporated into the average rockbolter when compared to a drill jumbo, maintenance takes longer, and more parts and components have to be replaced. Bolting units are exposed to falling rock, or cement from grouting, both of which impact upon maintenance costs. 25

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Significant Improvements When Atlas Copco introduced its new series of mechanized rock bolting units in late 2001, a wide range of radical improvements was incorporated. Based on the unique single feed system with cradle indexing, the new mechanized bolting unit, MBU, is considerably more robust, and less sensitive to falling rock, than its predecessor. Holes are easy to relocate, and the stinger cylinder improves collaring and the ability to install bolts under uneven, rugged roof conditions. Major re-engineering has resulted in 30% fewer parts. Less maintenance and stock inventory are required, and high availability has been recorded. Furthermore, the chain feeds used in the new Boltec series feature an automatic tensioning device, which guarantees even and strong feed force for the rock drill, while a stinger cylinder improves collaring and the ability to work under uneven roof conditions. The completely redesigned drill steel support provides sufficient space for bolt plates passing through, and facilitates extension drilling. The most outstanding benefit, however, is the computer-based rig control system, RCS. This system, which has already been successfully incorporated on the latest Boomer and Simba series of drillrigs, offers simplified fault detection, operator interactivity, and the basis for logging, storing and transferring of bolt installation production and quality data. The Boltec is equipped with the new rock drill, the COP 1532, which is short and compact, and features a modern double dampening system which, combined with the RCS, transmits maximum power through the drill string. The long and slender shaped piston, which is matched to the drill steel, permits high impact energy and long service life of all drilling consumables.

Versatility and Ergonomics Modern bolting rigs can handle installation of most types of rockbolts, such as Swellex, as well as resin and cement grouted rebars. Using the new 26

Boltec MC equipped with screen handling arm.

Boltec series based on RCS, the operator copes easily with the more demanding cement grouting and resin cartridge shooting applications, by controlling all functions from the cabin seat. Up to 80 cartridges can be injected before the magazine needs refilling. Also, because meshing is often carried out in combination with bolting, an optional screen arm can be fitted parallel to the bolt installation arm, to pick up and install the bulky mesh screens. Up to 10 different preprogrammed cement-water ratios, and various additives, can be remotely controlled. The new generation rigs offer the operator a modern working environment in a safe position. Low positioned, powerful lights provide outstanding visibility of the entire drilling and bolting cycle. The new Boltec family has two members: the Boltec MC, for bolt lengths of 1.5-3.5 m and roof heights up to 8 m; and the larger Boltec LC for bolt lengths of 1.5-6.0 m, primarily for large tunnelling projects having roof heights of up to 11 m. The initial positive response from operators and mechanics confirms that the new generation of Boltec will pave the way for further acceptance of mechanized bolting.

Screen Installation In Canadian mines the combination of rockbolts and screen, or wire mesh, is commonly used for rock support. Since rock reinforcement is potentially one of the most dangerous operations in the work cycle, mechanized rockbolting has become more popular. A computerized Boltec MC, equipped with screen handling arm, has been in use for a couple of years at Creighton Mine, installing screen with split-set bolts. In general, the screen is 3.3 m-long x 1.5 m-wide, and is installed in both roof and walls, down to floor level. Typical spacing of bolts is 2.5 ft. Three different types of bolts are used, depending on rock conditions, and all bolting must be done through the screen, with the exception of pre-bolting at the face. In general, galvanized split-set are used for wall bolting, while resin grouted rebar or mechanical bolts are used in the roof, and Swellex in sandfill. Once the screen handling arm has picked up a screen section and fixed it in the correct position, the powerful COP 1432 hydraulic rock drill quickly completes the 35 mm diameter, 6 ft and 8 ft holes. The bolting unit remains firmly fixed in position after the hole is drilled, and the cradles are indexed, ROCK & SOIL REINFORCEMENT

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moving the bolt, with plate, into position. The bolt feed, combined with the impact power from a COP 1025 hammer, is used for installing split-set bolts. The complete rock reinforcement job is finished in just a few minutes.

Cabletec Simba

Boltec MC Flexibility The Boltec MC delivered to the Creighton mine is capable of handling several types of bolts: split-set, mechanical-anchors, resin grouted rebar and Swellex. The switch of accessories between different bolt types takes 5-10 minutes. To minimize water demand during drilling, water-mist flushing is used. The Boltec MC can also be equipped with a portable operator’s panel connected by a 50 m-long cable. Cartridge shooting is remote controlled for the Boltec MC, and up to 80 cartridges can be injected before refilling is needed. A unique feature is the possibility to use two different types of cartridges, with fast or slower curing times, housed separately in the dual cartridge magazine. The operator can select how many cartridges of each type to inject into any hole. For instance, he can inject two fast curing cartridges for the bottom of the hole, and follow up with slower-curing cartridges for the rest of the hole, all without leaving his operator’s panel!

Cabletec L for Cable Bolting Atlas Copco has developed a fully mechanized rig for drilling and cable bolting by a single operator. The first unit is in operation at Outokumpu’s Kemi chromite mine in northern Finland, and a second unit has gone to Chile. The Cabletec L is based on the long hole production drilling rig Simba M7, with a second boom for grouting and cable insertion. The booms have an exceptionally long reach and can drill a line of up to 4.7 m of parallel holes from the same rig setup. Likewise, the booms can reach up to 7.8 m roof height, allowing the Cabletec L to install up to 20 m-long cable bolt holes in underground mining applications such as cut and fill mining and sub level stoping. Furthermore, the ROCK & SOIL REINFORCEMENT

Stoping sequence at Kemi underground mine. Cabletec drilling upwards, and Simba drilling downwards.

drill unit can rotate 360 degrees and tilt 10 and 90 degrees, backwards and forwards respectively. The new rig is designed on proven components and technology featuring two booms - one for drilling and the other for grouting and cable insertion. It also features an on-board automatic cement system with WCR (Water Cement Ratio) control. All these features facilitate a true single operator control of the entire drilling and bolting process. The two boom concept has drastically reduced the entire drilling and bolting cycle time and, by separating the drilling and bolting functions, the risk of cement entering the rock drill is eliminated. The operator is able to pay full attention to grouting and cable insertion, while drilling of the next hole after collaring is performed automatically, including pulling the rods out of the hole. Cabletec is equipped with the well proven COP 1838 ME hydraulic rock drill using reduced impact pressure with R32 drill string system for 51 mm hole diameter or R35 for 54 mm holes. Alternatively, the COP 1638 rock drill can be used. Maximum hole length is Cabletec main technical data Length:

13.9 m

Width:

2.7 m

Height:

3.3 m

Turning radius: 4.3m / 7.5 m

32 m. The cable cassette has a capacity of 1,700 kg and is readily refilled thanks to the fold-out cassette arm. The cement mixing system is automated, comprising a cement silo containing 1,200 kg of dry cement. The cement is mixed according to a pre-programmed formula, resulting in a unique quality assurance of the grouting process. The cement silo capacity is adaptable for up to 20 m-long, 51 mm-diameter holes. To date, most holes have been drilled in the 6-11 m range, for which the rig has grouted and installed cable at a rate of more than 40 m/h. Depending on type of geology and hole diameter chosen, the drilling capacity can vary between 30 and 60 m/h.

Conclusion Rock support, including scaling, bolting, screening, and cablebolting, is still the bottleneck in the working cycle in underground mining and tunneling applications. Clearly, any reduction in the time required to install the necessary support has a direct impact on the overall cycle time, and consequently the overall productivity and efficiency of the operations. The fully mechanized bolting rig of today, incorporating all of the benefits of modern computer technology, constitutes a major leap towards improved productivity, safety and operator environment.

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Using Rocket Boomers to Install Rockbolts Adaptability for Drilling and Installation When a contractor undertakes an underground drill/blast excavation project, it is of utmost importance to have the most suitable equipment available, both for blast hole drilling, and for rockbolt drilling and installation. For most situations, the Atlas Copco Rocket Boomer is the best possible unit to choose. This is true, not only for its drilling capacity, but also for its adaptability to semi-mechanized installation of some of the most frequently used rock bolt systems, such as Swellex rock bolts and MAI Self Drilling Anchors (SDA). This affords the contractor the option of using a single drillrig to cover all face drilling and rockbolt installation operations. On some contracts, this can make the difference between profit and loss. On bids, it can provide the margin for the contractor that swings the award.

Swellex Rockbolts

Atlas Copco Rocket Boomer, with its very capable BUT booms, is suitable for all kinds of rock reinforcement.

with Swellex chuck, or, for mechanized insertion, the new Swellex chuck mounted on the COP hammer. For mechanized handling of the drill steel, a Rod Adding System (RAS) can be mounted on the feed. For semimechanized installation, the following cycle of operations can be used: select a drill steel length that is slightly longer than the length of the bolt to be installed; drill the bolt hole at the chosen spot, and to the full length;

keep the feed at the drill hole, and recover the drill steel by the RAS grippers; attach the Swellex chuck to the COP hammer; manually locate the Swellex bolt with faceplate in the drill steel support at the top; insert the Swellex bolt into its final position in The new Atlas Copco Swellex Pm24C and Mn24C features improved work absorption capacity by way of elongation and load taking.

Regardless of manufacturing origin, installation of rockbolts of lengths of 4 m and upwards is normally a heavy and troublesome operation. The Swellex Pm24 or Mn24 rockbolt is no exception. However, by adding a few optional items, a standard Atlas Copco Rocket Boomer can be modified to take care of most of this work. It will insert the Swellex Pm24 or Mn24 into the hole, fully inflate it to optimal capacity, and even test it! Not only is it quick and easy, but also safer than the traditional manual method. Top of the list of optional components is a service platform to assist with the high level holes. An onboard Swellex hydraulic pump is advisable, and, for manual insertion, a Swellex handle 28

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1. The first SPEEDROD is drilled into the rock.

1

2. The gripers lift the second rod into place and drilling continuous. 3. When the hole is finished, the RAS system uncouples and removes the rod.

2

using the feed and the COP rock drill; grip the bottom of the string with the BSH 110, and attach the bottom end section of the connectable Swellex, with faceplate; feed it into place using the rock drill and Swellex chuck; connect the Swellex pump, and inflate the bolt. It will take a few seconds to fully expand the complete bolt. When the pump stops, the bolt is ready to take its full 24 t load.

Swellex Hybrid 3

Mechanized Road adding RAS.

the drill hole, using the feed-force from the hammer; and inflate the Swellex bolt using the on-board hydraulic Swellex pump. All done, and ready for the next bolt!

Connectable Swellex When there is a need for very long bolts to be installed in a narrow drift, tunnel or cavern, the solution can be the Swellex Pm or Mn 24C connectable rock bolt. This system comprises three different types of bolt section that can be combined to practically any required length. Each of these three sections is characterized by its function. The first section is sealed at its top end and threaded at its bottom end. The middle sections are threaded at both ends, and the bottom section is threaded at one end and designed to fit into the Swellex chuck at the other. The sections are threaded together to form a tight connection. Installing Swellex Pm or Mn 24C utilizes the same optional components as for the installation of long Swellex bolts, with the addition of either the BSH 110 Swellex version, or by using a Swellex retainer to keep the connectable Swellex in place when tying in Swellex sections. The RAS system can greatly assist handling of the Swellex Pm 24C or Mn 24C sections, using its two gripper arms attached to the BMH feed, which are remotely controlled by the Boomer operator. The bolt hole is drilled to full depth using extension ROCK & SOIL REINFORCEMENT

drill rods. Recommended drill hole diameter is 45-48 mm, with maximum 51 mm, using R28 drifter rods with a coupling diameter of 44 mm. The installation sequence is as follows: drill the bolt hole a little bit longer than the full bolt length; recover the drill string, and remove it from the feed; place the top-section of the Swellex Pm 24C or Mn 24C into the drill steel support, and feed the bolt section into the drill hole, either manually, or using the COP rock drill; grip the bolt with the BSH 110, or the retainer; thread in the required number of middle sections

The Swellex® Hybrid consists of a Swellex bolt coupled with one or more MAI Self Drilling Anchors (MAI SDA®). A special connection coupling welded on to the Swellex bolt, enables it to be inflated and the SDA portion to be grouted. After inflating the Swellex bolt, the rock mass between the face plate and the Swellex is pre-tensioned to the desired value. The rock mass is then exposed to confinement pressure and the hole annulus grouted through the centre hole of the SDA. In this way, the pre-tensioned support element is grouted for full protection and long lasting anchorage. Installation sequence of the new Atlas Copco Swellex Hybrid.

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Swellex® Hybrid rock bolts are recommended for rock support in tunnelling, civil engineering and mining applications where active (pre-tensioned) support is required to preserve rock mass structure, and grouting is needed for long life expectancy. The system is ideal in weak ground and around structural discontinuities. It is also recommended as a problem solver for long anchorage requirements.

Composition of the Atlas Copco Self Drilling Anchor (SDA).

Swellex Hybrid The Swellex ®Hybrid consists of a Swellex bolt coupled with one or more MAI Self Drilling Anchors (MAI SDA ®). A special connection coupling located between Swellex and SDA enables the Swellex bolt to be inflated and the SDA portion to be grouted.After inflating the Swellex bolt,the rock mass between the face plate and the Swellex is pre-tensioned to the desired value.The rock mass is then exposed to confinement pressure and the hole annulus grouted through the centre hole of the SDA. In this way, the pre-tensioned support element is grouted for full protection and long lasting anchorage.

Swellex Hanger Swellex® Pm 24H is a versatile rockbolt having a flanged head which has a female M30 or M36 thread. The bolt

Atlas Copco SDA system is built around the Boomer, with add-on standard options, and backed up by Atlas Copco worldwide presence, know how and support.

has a static load carrying capacity of 200 kN and is designed for hanging services while reinforcing the rock. After the bolt has been installed by using an inflation adapter, a forged eyebolt (M30/M36) is screwed on. Utilities can New Swellex PM24 Hanger rockbolt.

then be suspended directly from the eyebolt. The bolt, with faceplate, becomes part of the rock support pattern, with all the advantages of Swellex. Swellex® Pm 24H hanger rockbolts are recommended for rock support in tunnelling, civil engineering and mining applications where suspending utilities in an underground excavation is needed. The bolts are designed as anchor points for hanging utility pipes, ventilation columns and rails, while at the same time reinforcing the rock. Cables can also be passed through the eyebolts to form lacing or trusses in rockburst prone ground, or to reinforce friable or weak formations. Swellex® Pm 24H can be installed using a standard Swellex pump combined with an inflation adapter.

Self Drilling Anchors System In 2002, Atlas Copco incorporated the MAI series of rock bolts into its product range. Products like MAI Self Drilling Anchors (SDA) can be used in ground formations that are so soft, 30

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BSH 110 The BSH 110 is a hydraulic drill steel support providing gripping and guiding functions. The BSH has to be equipped with the rubber bushing and steel bushing halves to match the SDA dimension. The standard BSH 110 will manage anchors up to size R51. There is also a special version, BSH 110 available for SDA installation, which minimizes the part of the bolt protruding from the rock and can fit SDA bars up to the dimension of T76. All versions of BSH 110 have to be equipped with special SDA bushing halves when handling SDA. Atlas Copco semi-mechanized MAI bolt installation from a Rocket Boomer.

Installing SDA fractured, or weak that a normal drill hole will collapse before a standard rock bolt can be inserted. The SDA system comprises standard items like the sacrificial bit, a variety of bolt sections, couplings, faceplate and spherical nut. Atlas Copco has developed some components and functions for the Rocket Boomer to make it the perfect tool for installing SDA. The standard feed on the Boomer should be equipped with the new BSH 110 drill steel support. This is used to guide the bolt when drilling, and when extending the SDA bolt sections. The new BSH 110 is designed to leave a minimum of the bolt protruding from the rock face, thus utilizing the full length of the installed bolts. The BSH 110 has remote-controlled functions for guiding, gripping and drilling, giving the operator full control of the bolting sequence from the drilling position. The BSH 110 is fully compatible with any BMH 6000 feed. For those worksites where a lot of SDA drilling will be done, the COP 1238 or COP 1838 rock drills can be fitted with a special SDA shank adapter and a conversion kit. The SDA shank adapter has a female end to eliminate the need for a loose coupling sleeve, saving time when unthreading the bolt. This makes handling easier when extending the SDA bolts, boosting productivity and improving safety. At work sites where SDAs are not in daily use, a suitable solution is to use a shank connector to simplify the handling of ROCK & SOIL REINFORCEMENT

SDAs on a standard Boomer. The shank connector is added to the shank adapter on the hammer, and should be chosen to match the thread that is used on the SDA. Most frequently used threads are R32 and R38, but also combinations for the R51 and T76 SDA systems are available. Once the SDA activity is finished, the shank connector is removed and normal drilling can resume.

Most current rockbolt installation methods are manual. However, when the operation is assisted by a Rocket Boomer, productivity and safety are greatly improved. Using the optional equipment available for the standard Boomer, a typical SDA bolting semimechanized sequence will be as follows. 1) Modify the rock drill by attaching a suitable SDA shank adapter and

Length of anchor protruding after installation, depending on BSH 110 used.

SDA length outside tunnel face = 405

COP 1838

565

BSH 110B

256

SDA length outside tunnel face = 281 COP 1838

565

BSH 110SDA

301

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Two-man operation for simultaneous drilling and grouting of SDA using a Rocket Boomer and MAI m400NT grout pump.

an SDA COP kit that match the thread on the MAI SDA bolt. 2) Place the MAI bolt section on the feed with the selected MAI bit, and thread the bolt into the shank adapter female end. The BSH 110-SDA should be in position to guide the bolt. 3) Start drilling, and adjust the pressure to match the chosen bolt type and the prevailing ground conditions. Normally, the percussion pressure for SDA drilling is less than half, sometimes only one third, of the hydraulic pressure set for blast hole drilling. The SDA shank adapter makes it possible to drill the bolt close to the tunnel wall. 4) Grip the bolt with the BSH, and hold it in position while adding another MAI bolt section, prepared with a suitable anchor coupling. 5) Once the MAI bolt section is connected, open the BSH and continue drilling. When the last section of the MAI bolt is being drilled, the BSH 110-SDA should be fully opened, to allow the shank adapter to drill the MAI bolt deep enough to leave about 280 mm of the bolt protruding.

Suitable and flexible grouting units are the MAI M400 grout pump, and the Atlas Copco Craelius UNIGROUT E 22. The grout is pumped into the hollow MAI bolt, and is distributed through the MAI drill bit into MAI m400NT grout pump.

the drilled hole, filling cavities and cracks along the bolt. This completely fills the hole, forming a strong adhesion between the MAI bolt, the cured grout, and the surrounding ground formation. Once the grout has cured for 8-12 h, the MAI bolt can be post-tensioned to the required torque. However, MAI bolt installation can also be undertaken with continuous grouting, using a grout pump m400NT and the new integrated injection adapter - Ceminject. There is usually a need to alternate between flushing with water and grout. In underground installation, especially for radial bolting, it may be inconvenient to do the grouting during drilling as this may create a mess of grout on the feed, and make it difficult to remove excess grout mix used for flushing. The alternative method offered by the Ceminject system is to flush the borehole with water while drilling the SDA, and to commence grouting only after reaching the design depth, while maintaining a slow rotation mode of the bolt still fixed to the drifter. This ensures good in-situ mixing and penetration of the grout around the bolt, optimizes the friction contact with the rock/soil, and reduces wastage of grout mix.

by Olle Karlsson Installation of anchor system using a Rotary Injection Adapter.

Grouting SDA The installation sequences described above use water flushing for drilling. The commonly used method for MAI bolts is post grouting. This is carried out manually from the Boomer basket, or any other service platform, by connecting a grouting unit to the protruding end of the MAI bolt. 32

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Connectable Swellex Alternative to Cable Bolts The Mn24C connectable rock bolt is a relatively new addition to the Swellex family. With a profile made of Mn24 tubing, the sections of Mn24C are coupled together with threaded connections that can support loads at least as high as the profile strength. Through an ingenious assembly, the Mn24C combines the exceptional ease of installation of Swellex with the length capability of coupled bars or cable bolts. Advantages of Mn24C rockbolts are ease and speed of installation, and quality assurance of installation and performance. Many mine operators already consider Connectable Swellex Mn24 to be the best solution to their ground control problems in stoping. Although manual installation does not appear attractive on a large scale, operators are extremely interested in replacing their time consuming cable bolting operations with the simpler and safer Swellex system. With a semi-mechanized installation, Connectable Swellex is very competitive, and is deemed profitable in both North America and South America.

Swellex Mn24C threaded connection was launched in 2003.

total cost ranged between C$13/m and C$35/m, a high standard deviation that can be explained by disparities in the costing systems across the sample mines. The market for very long cable bolts is not targeted, as longer bolts are usually installed by mechanized means. However, while the time

saving is sizeable with long cable bolts, it is not appreciable with lengths of less than 8 m-10 m, when Mn24C becomes a good alternative.

Time is Money A comparison has been made for typical underground mining practices,

Installing Connectable Swellex into a pilot drive.

Market Study The following conclusions resulted from a market study performed in 1995 in Canada on 71 responses from 109 underground mines, some 68 of which are mining metal and industrial minerals, excluding potash and salt. The most-used mining method reported was longhole stoping, followed by Vertical Crater Retreat, Sub-Level Caving and Cut & Fill. An estimated 870,000 m of cable bolts are installed every year in Canada’s hard rock mines. Most mines using cable bolts range in output between 1,000 t/day and 5,000 t/day. The average total cost of drilling and installing the cable bolts was reported at C$23.00 ± C$6.60/m. However, ROCK & SOIL REINFORCEMENT

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Table 1. Comparison of typical installation performances for Cable bolts and Mn24C. Cable Bolts Manual Installation

Cable Bolts Manual Installation

Mn24C Manual Installation

Mn24C Semi-Mechanized Installation Drilling – Installation Separate

Mn24C Semi-Mechanized Installation Simultaneous Installation

Calculation Base: 40 double Cable bolts 6 m long

Calculation Base: 60 single Cable bolts 6 m long

Calculation Base: 60 Connectables 6 m long

Calculation Base: 60 Connectables 6 m long

Calculation Base: 60 Connectables 6 m long

Drilling (Long Hole): 1.3 shifts x 1 man 64 mm diameter holes

Drilling (Long Hole): 1.4 shifts x 1 man 50 mm diameter holes

Drilling (Long Hole): 1.4 shifts x 1 man 50 mm diameter holes

Drilling (Long Hole): 1.4 shifts x 1 man 50 mm diameter holes

Drilling (Long Hole): 1.4 shifts x 1 man 50 mm diameter holes

Installation: 2 shift x 2 men

Installation: 3 shift x 2 men

Installation: 2.3 shift x 2 men

Installation: 2.3 shift x 1 man

Installation: 1.4 shift x 1 man

Grouting: 1.25 shift x 2 men

Grouting: 2.6 shift x 2 men

Details: installation time is 10 min. and is performed after all the holes are drilled.

Details: installation time is 10 min. and can be performed between each hole drilled.

Plate tensioning: 0.5 shift x 2 men

Plate tensioning: 0.5 shift x 2 men

Total: 9.8 man-shifts

Total: 13.6 man-shifts

Total: 6.0 man-shifts

Total: 3.7 man-shifts

Total: 2.8 man-shifts

Elapsed time: 5.0 shifts

Elapsed time: 6.0 shifts

Elapsed time: 3.7 shifts

Elapsed time: 3.7 shifts

Elapsed time: 2.8 shifts

Supplies: cables, grout tube, grout, plate, barrel and wedge

Supplies: cables, grout tube, grout, plate, barrel and wedge

Supplies: Connectables, retainers, plate and $0.50/m for seals and pumps parts

Supplies: Connectables, retainers, plate and $0.50/m for seals and pumps parts

Supplies: Connectables, retainers, plate and $0.50/m for seals and pumps parts

Drilling costs: $5.80/m Supplies cost: $8.50/m Install.: $11.20/m ($45/h)

Drilling costs: $5.00/m Supplies cost: $6.40/m Install.: $12.20/m ($45/h)

Drilling costs: $5.00/m Supplies cost: $17.00/m Install.: $4.60/m ($45/h)

Drilling costs: $5.00/m Supplies cost: $17.00/m Install.: $2.30/m ($45/h)

Drilling costs: $ 5.00/m Supplies cost: $ 17.00/m Install.: $1.40/m ($45/h)

Total: $25.50/m

Total: $23.60/m

Total: $26.70/m

Total: $24.40/m

Total: $23.40/m

installing manual or semi-mechanized cable bolts, using a 40 double strand cable bolts block or a 60 single strand cable bolts block. It was assumed that the support capacity required by the designed pattern of double strand cable bolts would be met by an array of 60 Mn24C rockbolts. The cost analysis presented in Table 1 shows that, in a semi-mechanized installation, using Mn24C rockbolts to replace short cable bolts of less than 8 m-long saves a good deal of time. In addition, quality control is better, and training is very simple. Analysis of Table 1 shows also that, for an Mn24C price of C$16.50/m for the bolts, the combined system would have an 34

operating marginal cost similar to cable bolts. Increase in productivity still has to be analyzed in term of costs saving.

Conclusion Productivity and costs analyses have also been carried out to assess the competitiveness of the Mn24C rockbolts with cable bolting. Field testing in Canadian mines demonstrated higher productivity in ore extraction and development, due to the flexibility of installation of the Mn24C bolts. Perfect installation by non-specialized crews, with immediate support over the entire length of the bolt, contributed to a higher

efficiency. Quality of installation was not jeopardized by geological cracking and voids, or water, and there was no wait for curing before tensioning. The increase in productivity can be utilized to accelerate development of stopes, adding flexibility to mine planning, and facilitating the timely extraction of ore and its delivery to the mill. The added productivity would also mean less overtime and scheduling conflicts. To summarize, Mn24C is not only a very efficient means of ground support, it also underpins a smooth mining operation.

by François Charette ROCK & SOIL REINFORCEMENT

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Rockbolt Corrosion in Mining and Tunnelling Observing Corrosion The phenomenon of corrosion of rockbolts in an underground environment is a subject that is attracting more and more attention from engineers and project owners. Field observations have shown that, in some conditions, unprotected rockbolts corrode freely and rapidly. A closer look at the overall conditions at monitored sites highlights the difficulty in predicting the life of the bolts. Often, water conditions are not taken into account. Although water supply can be non-corrosive at source, the process of recirculating water often gathers corrosive ions, and renders the water more aggressive toward steel components. At Atlas Copco, it was recognized that theoretical predictions of a rockbolt’s life could only be a first assessment of applicability of non-protected ground support. Ultimately, extra protection is needed to isolate the rockbolt from an aggressive environment. This can increase the effective life of the ground support, and secure its long-term performance. Observed field performance in known conditions can provide an extremely instructive insight of the global corrosion process, and on the means to alleviate its effect on ground support.

Corrosion Underground Corrosion can be either uniform on the exposed steel surface, or very localized. Uniform corrosion is characterized by a regular loss of metal from the corroding surface, while localized corrosion will produce metal loss in a very confined area of the exposed surface. Under uniform corrosion, a rockbolt will be radially thinned from the outside or the inside, or, in the case of split tube stabilizers, from both sides. Localized corrosion by pitting can be seen in areas where the bolt surface is ROCK & SOIL REINFORCEMENT

Figure 1. Pull testing to verify long term mechanical properties of Swellex rockbolt.

metallurgically non-homogenous, or where certain types of rock minerals are in contact with the bolt. Crevice corrosion can occur with confined and closely spaced metal surfaces, such as at the interface between bolt collar and face plate. It has also been observed that, in highly corrosive environments, uniform and localized corrosion can occur simultaneously. Galvanic corrosion is another type of corrosion where dissimilar metals are in contact in the presence of an electrolyte, either liquid water or vapour. A more appropriate description may be bimetallic corrosion. Graphical representation of the types of corrosion likely to attack rockbolts is presented in Figure 2, modified after Dillon (1982). In the main, environmental factors will determine the type of corrosion and the mode of attack. From the point of view of mechanism of attack, there are two main modes of attack in underground environments: corrosion in water, where the bolts are in contact with running water; and atmospheric

corrosion, where aggressive airborne contaminants are deposited on rockbolts and any metallic surfaces. Water inflow, chemicals in water, microbial species, and fumes from both diesel engine exhausts and explosive blasts, are the most common factors that will impact on the corrosion rate of rockbolts. Level of isolation from external agents will also determine the rate of corrosion. The major blame for corrosion in water lies with chloride and sulphate ions. Very high concentrations of these ions have been measured in both civil engineering and mine tunnels, all over the world. Iron sulphide minerals, principally pyrite and chalcopyrite, are present in most metal mines, whereas an extremely high chloride and sulphate ions concentration is more typical of Australian mines. Oxidation of pyrite produces sulphuric acid, and mine waters with pH as low as 2 can be produced. Also, water flow, and changes in ions concentration over time, will affect passivation. Use of recirculated water increases the potential for corrosion problems. 35

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Figure 3. Fibre optics borehole endoscopic camera.

Figure 2. Types of corrosion encountered on rockbolts (from Dillon 1992).

Corrosion Potential Queries about the life expectancy of rockbolts are frequently received by Atlas Copco from its customers. While the only way to assure long-life performance under aggressive conditions is to coat the bolt to isolate it from the environment, the need to know the expected life span in temporary bolting applications has stimulated research and development in the Rock Reinforcement group. A new approach was elaborated, consisting of three steps that allow a high level of control on the bolt’s performance. First, preliminary analysis of corrosion potential is carried out, using field data and standards in the field of

corrosion, such as DIN 50 929. This first step allows the tunnel owner, or mine operator, to make a first decision on the need for corrosion protection. Next, during the operation of the tunnel or mine, regular testing can be performed, in order to assess the real corrosion rate of the rock support. Third, if the tests showed that the environment is corrosive enough to reduce the effective life below that required by the customer, the use of a corrosion protected Coated Swellex is recommended. Table 1 presents theoretical corrosion rates calculated with the norm DIN 50 929 for underground sites in Sweden, Japan, Canada and Australia. Typical tests performed include water

Figure 4. Snapshot of inside view of Swellex bolt with borehole camera – no corrosion visible inside the Swellex profile.

36

analysis, destructive pull tests and profile endoscopy with a fibre optics borehole camera (Figure 3). Figures 4 and 5 show the interior profile for two Swellex bolts, corroded and non-corroded. Pull tests, performed with the equipment shown in Figure 1, will provide an index of load capacity at the collar of the bolt. It has been observed with the borehole camera that corrosion is limited to the first 30 cm from the inflation bushing, so the loading capacity of the bolt inside the rock mass is almost always kept above its rated value. In relatively nonaggressive environments, non-coated Swellex bolts have proved to retain their minimum loading capacity for over 10 years.

Corrosion Protection Atlas Copco Coated bolts are covered with Corrolastic Expander Paint 839BX. This paint has been tested by

Figure 5. Snapshot of inside view of Swellex bolt with borehole camera – corrosion visible inside the Swellex profile.

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Table 1. Corrosion Rate Assessment of Unprotected Steel for Underground Sites Using DIN 59 929 Sites

Ca (mg/l)

Cl (mg/l)

SO4 (mg/l)

HCO3 (mg/l)

pH

Assessed Corrosion Rate German DIN 50 929 for Uniform/Pitting (mm/year)

Mine A Canada

600

540

1610

NA

7.8

0.1/0.5

Mine B Canada

540

870

61700

NA

3.4

More than 0.1/0.5

Kapuzineberg Sweden

22

2661

1.3

NA

6.95

0.1/0.5

Ritto Japan

13

2

3

52

6.7

0.1/0.5

Aspo Sweden

N/A

N/A

N/A

N/A

N/A

0.1/0.5 for non-coated 0.02/0.1 for Coated Swellex

Mine C Australia

140

1200

420

100

7.9

0.05/0.2

Mine D Australia

350

10

8300

38

3.0

0.1/0.5

the Swedish Corrosion Institute in extremely aggressive environments, and proved not to be affected by high chloride or sulphuric acid levels for periods over 10 years. In Table 1, the Swedish Corrosion Institute has assessed that the life span (at Aspo) of a Coated Swellex in a very aggressive environment would be of more than 20 years. The most critical parameters in corrosion protection are the characteristic corrosion sensibility of the coating, and the physical state of the coating with reference to scratches and indentations. Tests performed by the Swedish Corrosion Institute for Swellex immersed in sulphuric acid have shown that, while the corrosion rate of unprotected Swellex would be 0.5 mm/year in the simulated environment, the Coated Swellex showed no traces of general corrosion, and pitting at scratch locations stayed very localized. In these conditions, corrosion in unprotected areas would not migrate to a protected area, the coating minimizing corrosion and controlling its spread. It has been demonstrated that corrosion is a very complex process, and corrosion rates are very hard to predict

accurately. However, predictive methods can be helpful to evaluate the need for corrosion protected rockbolts. Field observations, followed by protective coating of the rockbolt where necessary, can be used to control corrosion, both in temporary and permanent rock reinforcement applications. This approach to corrosion of rockbolts has been developed by Atlas Copco to deal with the need for life expectancy assessment in the mining and construction industries.

Case Study at Aspo The 4 km-long subsea tunnel driven to access the site of the Aspo nuclear waste research laboratory at Oskarshamn, Sweden required some rock reinforcement, despite high quality rock over most of its length. In areas requiring support, rockbolts, rockbolts with wire mesh, and rockbolts with wire mesh and steel fibre reinforced shotcrete were used. Test drilling showed that rock reinforcement would get more difficult as the tunnel progressed, because fissure zones and saltwater leakage would place high demands on holding power

CORROSION POTENTIAL ASSESSMENT STEPS 1. PRELIMINARY ANALYSIS USING DIN 50 929 2. FOLLOW UP OF PERFORMANCE OF ROCKBOLTS – CAPACITY MEASUREMENT – ENDOSCOPY – WATER ANALYSIS TO MONITOR CHANGES IN CONDITIONS 3. RE-ASSESSMENT OF ADEQUACY OF CORROSION RESISTANCE TOOLS: WATER ANALYSIS, PULL TESTING, BOREHOLE CAMERA

ROCK & SOIL REINFORCEMENT

and corrosion resistance. At a depth of 300 m, the sodium chloride content of the seawater increases dramatically to 1.5%. Sydkraft Konsult chose Swellex for the job, because of their high degree of versatility and quality of installation. The corrosion protection on Coated Swellex met their demands for long duration use, and they found the quick and simple installation, with full support over the entire length of the bolt, extremely reassuring. Short 90 cm Swellex bolts were used for net fixing, and 2.4 m-long Swellex bolts were used for the main rock reinforcement duties. The views of the project management were borne out by a study carried out by the Swedish Corrosion Institute to estimate the risk of corrosion of Swellex rock bolts used at Aspo laboratory, from which the following conclusions were made. Bolts with an intact corrosion protection layer are not attacked for many years. In places where the layer is damaged, there is a risk for general as well as local corrosion. The attack will, however, be limited and, as such, less significant for the strength of the bolt. The time for fracture due to general corrosion for a 2 mm-thick bolt can be considerably longer than 20 years, mainly due to low oxygen content in the water. The attack will, however, be limited and, as such, be less significant for the strength of the bolt.

by François Charette 37

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Grouting for Support in Tunnels Eighty Years of Development Atlas Copco Craelius has been active within the area of grouting for over 80 years. The company originally started to develop and manufacture grouting equipment in an attempt to rescue expensive holes. These generally occurred when entering poor, fractured rock, in which the drill string showed signs of getting stuck, or flushing fluids were lost. Later on, grouting tools would accompany Atlas Copco Craelius diamond drilling equipment on large international tunnelling projects. Today, grouting encompasses so much more than traditional ground injection in tunnels, although it is still generally defined as an injection under pressure of fluid material into fractures and cavities in rock, soil or artificial structures. Depending on the composition and mix of the injected material, it will react physically and chemically to stabilize, strengthen, or seal the ground or the structure. In Scandinavia, the lower cost of tunnels compared to the rest of Europe is not only due to better rock quality, but also because grouting is classified as part of the support. It is generally accepted that high grouting pressure, developed primarily by the French for use in the Alps, increases the grouted volume and strengthens and seals planes of weakness. Better economy is expected using high pressures, by way of reduced drilling costs and a higher output of fresh, stable grout, especially when using microcements. Low pressure grouting, developed by the Americans for the sedimentary formations in the USA, and by the British in the coalfields, is designed to avoid further damage to the strata by cracking or widening existing cracks.

38

Cycle of events in face excavation and support.

Drilling for Grouting in Tunnels Grouting is often considered as a hindrance in the progress of the tunnel advance. Instead it should be seen as a tool for the next step, and as one of the most important parts of the final rock support. The intention is to use the cement to stabilize, strengthen or seal the ground mass around the tunnel. It is a waste of time and money to blast and excavate the rock far outside the required profile, and then replace overbreak with concrete. Grout holes for pregrouting in tunnels are 15-25 m-long, and should end 3-4 m outside the theoretical contour,

and with a maximum deviation of 3-5% from the intended target. This involves starting with guide rods, and then using a rod adding system. Bigger rod sizes are needed to ensure better stability compared to blast hole drilling. The diameter is normally 51-64 mm. When the ground is of poor quality, it is harder to drill the holes, and the need to drill straight holes is much greater. In such ground it is also essential to place the grout where it is required. Where possible, grout holes should be drilled at right angles to the main fissures, in order to intercept as many as possible. This is important when post-grouting in tunnels, as well as in traditional surface grouting. ROCK & SOIL REINFORCEMENT

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contact grouting method also serves to seal the joints between the lining segments.

Pregrouting

Grouting of the curtain cone.

This demand is difficult to meet when pre-grouting in tunnels, where spacing is reduced to ensure that fissure planes, with an unfavourable orientation to the grout holes, will be grouted properly. Here, the diameter of the drillhole has very limited influence on the grouting result. Because of the stiffness of the drill string, larger hole diameters in general result in straighter, albeit more expensive, holes. The setting of packers is more expensive and difficult in large diameter holes, as is the grouting. General requirements for drilling equipment in tunnelling work are as follows. If possible, drill all holes from a single set up, and with two different rod sizes and three different hole diameters for blast hole, cut hole and grout hole. Use a service platform and a rod adding system (RAS) with rod magazine: drilling for a grout round may involve handling some 5 t of drill steel. A positioning control instrument is a necessity, together with good working lights, and an elevated sound-protected cabin for full view of the face. A stepless mix of flushwater and air is advisable, bearing in mind that one drill rig uses 200-300 lit/min of water. High pressure cleaning equipment will be necessary for the grout holes and the drilling and grouting equipment. Grouting is too often planned and carried out as an off time shift, when the drilling equipment is elsewhere. Thus, when there is a need for additional grout hole drilling, this cannot be undertaken immediately. Consequently the driller cannot easily pass his information and observations to the grouting technician. ROCK & SOIL REINFORCEMENT

Grouting in Tunnels Tunnels are constructed for many different purposes, and under widely varying geographic and geological conditions. Tunnels carrying fluids, be it fresh water or sewage, should not leak; and all tunnels should resist the inflow of water from the surrounding ground. The latter requirement may be necessary to avoid draining natural water into the tunnel, which could lead to a general lowering of the ground water table in a wide area above its alignment. Movement of the water table may result in subsidence and damage to existing surface structures, loss of capacity of drinking water wells, and similar undesirable consequences. In other instances, especially in unstable ground containing running material under pressure, or in karst formations, grouting may be necessary to stabilize, strengthen and seal the strata. Tunnels that have to be watertight, as well as tunnels in weak ground that have to have a long service life, are usually lined. This lining is often placed concurrently with the tunnelling process itself, particularly in TBM bored tunnels where it is constructed of rings of prefabricated segments. Even in bored tunnels, where the excavated shape and diameter are controlled within narrow limits, there will be a slight annular gap between the outside of the lining and the inside of the bore. Grouting behind the lining serves the purpose of filling this gap, so that the lining will support the ground from the beginning, without settlement. This

The cost for pregrouting can be 5-10 % of the cost of postgrouting for reaching comparable and satisfactory results. The main reason is that both the grout pressure and the grout flow can be fully utilized in undisturbed rock whereas postgrouting always is done against a free surface, often cracked up from blasting and excavation. Investigation drilling is done during the actual tunnel work and parallel with the pregrouting in order to investigate the rock properties, like cracks, fissures and fissure systems, occurrence of water, and soft or weathered rock, for the next 50 metres or so. Pregrouting means that the rock is treated ahead of excavation. These two operations are repeated until a satisfactory result is achieved. The pregrouted zone should always go beyond the area that is disturbed by blasting, bolting or excavation. Grouting and pregrouting of tunnels have three different purposes: stabilization, strengthening and sealing of the ground. Stabilization grouting creates a skeleton of grout in weak parts or areas of the rock, to avoid sliding in cracks, fissures or bedding planes. This type of is grouting is to support a temporary construction or when a concrete casting is done at a later stage. Strengthening grouting is done for reinforcing a tunnel permanently. In most cases it is less expensive to utilize and strengthen the existing rock structure compared to replacing it with a new construction of concrete. Sealing grouting is strengthening grouting developed to almost water tightness. Sealing grouting is divided into different sealing classes depending on permissible water inflow. In Scandinavia normal tunnels are said to present insignificant problems when the leakage is in the range of less than 5 lit/min per 100 m. If it exceeds 10-20 lit/min per 100 m, then significant problems will occur. 39

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Drammen Case Study At the Norwegian port of Drammen, a second single-tube 2.3 km-long tunnel with bi-directional traffic flow was required to relieve congestion on the north bank of the river. The tunnel is on a curved alignment beneath the Bragernes Ridge, an outcrop of igneous rock comprising 50% porphyry and 50% basalt. The main face had an excavated arched cross-section of 70.5 sq m, which included a large drain. The main contractor was Selmer, for client Statens Vegvesen Buskerud, the local agency of the Norwegian State Highways Authority. A condition on the construction of the tunnel demanded that there be no interference with the water table, and the tunnel itself be kept dry. The maximum ingress of water allowed before grouting was 30 lit/min/100 m towards the tunnel ends, and 10 lit/min/100 m in the centre section. The grouting sequence commenced with the drilling of 27 m-long, 51 mmdiameter holes ahead of the face to test for water. These were drilled by an Atlas Copco Rocket Boomer 353S, using threaded extension steel, which was manually attached. Generally, ten forward holes were drilled, with a 10 m overlap, allowing 17 m advance between events. The contract envisaged injection of 2,370 t of grout to achieve the objective

water flows, a major operation for which Selmer invested in a sophisticated Atlas Copco Craelius truckmounted Unigrout E 400-100 WB. This comprised a containerized mixing and pumping plant with external cement feed and additive hoppers, and liquid additive tank. Inside the container were two Cemag units, and two 400 lit/min Pumpac units, with a single 400 litre Cemix WB weight batching mixer. The unit’s nominal capacity is 4 t/h of dry cement, but up to 66 t of cement was successfully injected into a particularly wet round over a 15 h period.

Pumping and Logging The Atlas Copco Craelius Pumpac System is based on a double acting pump principle. The system has been made simple and user-friendly by way of modularized parts, independent and stepless variable pressure and flow, easy and fast change of valve assembly units, and environmentally friendly hydraulic fluid. Then the whole life cost is kept to a minimum by system adaptability. The system features a hydraulic switch-over system, integrated in the hydraulic cylinder, and a split cotter fast-locking system of the two piston rods for easy dismantling of the cylinder assembly. Three sizes of electric motors are available: 7.5 kW, 15 kW and 22 kW. There are

Container mounted grout mixing and injection system to be carried on a truck.

two sizes of grout cylinders: 110 mm and 150 mm diameter; and two types of valves: ball valves for normal grouting applications, and disc valves for when a smooth flow and minimal pressure drop are required. Maintenance is easy, by way of a self cleaning cement fluid end, water flushing of cement and hydraulic piston rods, and only one 46 mm wrench for servicing the cement pump. The Logac system is a computer based logging system for sampling and storing of data during the grouting operation. The recorder is housed in a cabinet with a Craelius Flow Pressure (CFP) meter unit equipped with cable and quick coupling for easy connection. The CFP meter unit consists of an electromagnetic flow-meter and a pressure-meter. The logged parameters are flow, pressure, volume, time, real time and hole number. The standard flow meter operates in a range of 0200 lit/min with a maximum pressure of 40 and 100 bar respectively. The standard pressure sensor covers a range of 0-100 bar. All parameters are shown in real time on the Logac 4000 recorder display, and stored on a PCcard. The Logac 4000 samples data six times per second, and stores it on the card every 10th second. The card can be kept as a permanent record for future references, or reused over and over again. The control panel consists of an on/off switch for the recorder, a display, a separate button for each of the eight groutlines, and a 10-key keypad. Each groutline shows time, real time, flow, pressure and volume. There is a button to show either one single line, or all eight lines simultaneously, and two diodes, one for telling when logging is on, and the other for informing when the memory card is 90% full. One reason for Selmer’s success at Drammen was that they could continuously pump high volumes of stable grout at high pressures. A normal pumping rate is 110-120 lit/min at 5060 bar, and they used 80 bar as stop criterion, and sometimes even 90 bar. The water/cement ratio ranged from 1.0 to 0.5.

by Sten-Äke Pettersson 40

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Rock Mass Stability with Swellex Early Strength Means Early Support According to Konda and Itoh, the rock mass in a tunnel is unstable between the face and 0.5D behind the face, regardless of rock types. Collapses occur most often when the stress/strength ratio of rock mass is smaller than 5, especially in sedimentary rock. Discontinuities, caused by joints in the harder igneous and metamorphic rocks, have also resulted in rock falls up to 0.5D behind the face. The risk of collapse in this area grows with increasing cross section of the tunnel. Steel Fibre Reinforced Shotcrete (SFRS) was recommended to increase the rock stability in the Tomei tunnel. The 28-day strength of this shotcrete was 36N/mm2, using a steel fibre mixture ratio of 0.7%. However, early strength would be required to give the necessary support. Unfortunately, attempts to increase the early strength of shotcrete may induce microcracking, with negative effect on the long-term stability of the concrete, particularly where the initial deformation speed of the rock is high. Without early shotcrete strength, rockbolts become the main support. However, since standard rockbolt grouting materials require time to harden, they don’t have much effect on the initial stability of the rock mass.

Tomei Study In a study on the Tomei tunnel in Japan, the influence on support of the rockbolt installation method was investigated by means of numerical modelling. It was found that the Swellex rockbolt exhibits more support effect right ROCK & SOIL REINFORCEMENT

Pull-out testing of rockbolts in the underground laboratory.

after installation, and also has greater control effect of displacement and rock mass plasticity, compared to grouted rockbolts. For stabilization of the region up to about 0.5D behind the face, the Swellex rockbolt is a more effective device than the grouted rockbolt. The Swellex rockbolt also has more control over the shear behaviour of joints compared to the grouted rockbolt, because Swellex exhibits support faster. As a result, it contributes to the formation of the natural arch, by improving stress continuity around the tunnel, as well as displacement control. Because one of the main roles of the rockbolt is to improve discontinuous rock mass to continuum, it can be

said that the Swellex rockbolt is very suitable for support of a discontinuous rock mass. Comparisons between 4 m and 6 m lengths of Swellex were also carried out. No difference in support effect between the two lengths was found, offering the possibility of shorter bolt lengths if Swellex is used. This is because Swellex completes the natural arch immediately after installation.

Numerical Modelling Face stabilization methods using Swellex at Tomei were also confirmed by means of numerical modelling. Tests determined the bonding stiffness and bond strength of Swellex and 41

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behind the face. At 10 m behind the face, 50 kN was generated at the crown and 131 kN at the sidewall. For both cases, loads on rockbolts do not increase more than 1D behind the face, due to the convergence tendency of rock mass displacement. Except for right after installation, axial force generated is about 1.5 times larger for Swellex than for grouted. Laboratory testing has determined the relationship between curing time and load capacity for grouted rebars.

grouted rockbolts as input for numerical modelling. Using these values, two-dimension and three-dimension models simulated pull-out tests. The rockbolt axial force generated at the tunnel crown in the case of grouted rockbolts was 1 kN immediately after installation, rising to 32 kN maximum. In the case of Swellex, 30 kN was generated immediately, rising to 38 kN. For Swellex, the axial force is more than 60% of the maximum value from the beginning, and is about 1.6 times that of grouted rockbolts. Overall distribution of rockbolt axial force was measured at 1 m, 10 m, 20 m, and 30 m behind the face. Using grouted rockbolts, almost no axial force was generated from crown to sidewall immediately behind the face. At 10 m (0.5D) behind the face, 30 kN was generated at the crown and 82 kN at the sidewall. Using Swellex, 33 kN was generated at the crown, and 66 kN at the sidewall right

Natural Arch The difference of crown settlements for grouted bolts and Swellex was 0.5 mm, 1.2 mm, and 1.5 mm at 1 m, 10 m, and 20 m behind the face, respectively. Using grouted bolts, a plastic region of about 4 m is generated from the crown to the sidewall section. In the case of Swellex, the plastic region near the crown tends to decrease, and the value is controlled at about 2 m. Where there is no support, the value is 6 m at the crown, and 4 m at the side wall section. The tunnel is stabilized by generating a natural arch of the surrounding rock mass, preserving its continuity for tangential stress. In the case of the Swellex rockbolt, since the continuity for ground stress of the arch section is greater than when using grouted rockbolts, it is thought to have a major effect on tunnel stabilization. Joint shear displacement is generated within 4.0 m of the tunnel profile, and this can be controlled immediately using a 4 m-long Swellex bolt. With grouted rockbolts, shear displacement

Displacement contour, rockbolt axial force, longitudinal, for grouted rebars.

42

extends to more than 4 m, due to the time lapse for grout hardening. When using Swellex rock bolts, maximum bonding with the strata is achieved right after installation, so the required bolt length is shorter than with grouted bolts.

Summary The excellent support effect of Swellex rockbolts can be summarized in four points as follows. Compared with grouted rockbolts, Swellex exhibits a much greater support effect right after installation, and contributes to stabilization of the rock mass near to the face. In a continuous rock mass, Swellex has a greater control effect over the plastic region. In heavily jointed rock, Swellex contributes more to the formation of the natural arch by controlling the shear behaviour of joints, improving the stress continuity of the rock mass. Swellex controls tunnel deformation better, and exhibits excellent support, making it superior to the equivalent grouted rockbolt. Because stabilization of the rock mass close to the face was a key point for the Tomei tunnel, Swellex rockbolts were specified. Swellex enables a tunnel structure to be stabilized by support, without the impediment of curing time for shotcrete and grouting materials. By installing Swellex bolts immediately after excavation, it is possible to avoid rock instability.

by Federico Scolari

Displacement contour, using shorter Swellex rockbolts.

ROCK & SOIL REINFORCEMENT

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Secoroc Uppercut – High Quality Tapered Equipment Designed for Pressure Increasingly powerful pneumatic and hydraulic rock drills place great demands on rock drilling tools, a fact that is well known to drillers working in mining and dimensional stone applications. This is the reality that has guided Atlas Copco Secoroc in the design of its range of Uppercut tapered equipment. At the heart of these innovative products there is a formidable steel grade and specialized manufacturing technique. The unique heat treatment process employed helps to release the internal stresses of the steel and give it greater bending resistance, while retaining high durability. The result is a tapered rod that’s better suited to the stresses and strains of modern rock drills. All in all, you won’t find longer lasting rods on the market today!

Tough Rods for a Tough Life Rods have a tough life, transferring the percussion energy from rock drill to bit, and then into the rock. They’re also subjected to high bending stress, not to mention corrosive water in the flushing hole. These harsh facts have not only guided Atlas Copco Secoroc in its selection of steel quality, manufacturing technique and heat treatment processes, but also in their decision to have a rolled-in stainless lining throughout the entire length of the flushing hole. Even the drifted flushing hole at the shank end is lined in the same way. The flushing hole is also protected by special anti-corrosion oil as standard, to prevent corrosion and risk of rod breakage. And for even greater protection, Uppercut rods have surface hardened shank and tapered sections for high wear resistance on those parts exposed to severe stresses during drilling. Secoroc tapered rods are already renowned for their superior fatigue

strength and resistance to bending stress, and, with the Uppercut range, have improved material properties still further.

Question of Degrees Different taper angles are used for different rock formations and rock drills. A wide taper angle is normally used when drilling with high impact hydraulic rock drills in medium hard to hard and abrasive rock formations. Taper angles of 11 degrees and 12 degrees are common on modern rigs. A narrow taper angle of 7 degrees is used for low impact rock drills and softer rock formations. This angle can also be used to counter spinning problems when using 11 degrees or 12 degrees equipment. In addition, a 4 degrees 46 minutes angle is available for very soft rock, to prevent bits from spinning or becoming detached when using pneumatic or hydraulic rock drills. Secoroc Uppercut rods are available with 22 mm hexagonal rod section and

Features of Secoroc Uppercut tapered rod.

ROCK & SOIL REINFORCEMENT

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range comprises button and cross-type bits in an extensive selection of design configurations. These designs can be used in a variety of rock formations for maximum productivity. Moreover, there are two new models, with an extra front button for improved hole straightness, higher penetration rate and longer service life. Furthermore, the Secoroc range of ballistic button bits is in the process of being extended to meet ever more diverse demands.

drilling costs, and is taking market share from integrals, especially in mining applications and the dimensional stone industry.

by Jan Lindkvist

The Secoroc Uppercut Rod ●

●

Prepared for the Future

Uppercut tapered rod and button bit ready to drill.

shank length 108 mm for 4 degree 46 minute, 7 degree, 11 degree and 12 degree tapers. Uppercut rods with 25 mm hexagonal rod section and shank length 159 mm are available with 12 degree taper.

High Performance Bits Secoroc bit design and production processes are in a state of constant refinement. The Secoroc Uppercut

Secoroc Uppercut tapered equipment can be used in all types of applications and rock formations. The lowest cost/metre drilled, a claim that has long been synonymous with Secoroc products, is now lower than ever with this range, along with higher drilling productivity. Tapered products, which first appeared on the scene in the 1960s, can readily handle the impact energy from modern pneumatic and hydraulic rock drills, while they are also ready to cope with the stronger rock drills currently on the drawing board. Nowadays, tapered equipment is favoured for increased penetration rate, longer service life and lower

●

●

●

●

Special anti-corrosion oil to protect the flushing hole of the rod Surface hardened taper end for high wear resistance and a longer service life Stainless steel flushing tube lining to prevent corrosion and breakage Drifted flushing hole with stainless steel lining at the shank end prevents breakage and increases service life Surface hardened shank end for high wear resistance and a longer service life Z708 steel for superior fatigue and bending strength

Range of Uppercut tapered rods and bits from Atlas Copco Secoroc.

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Speedy Rock Reinforcement Using Magnum SR Thread System for the Future The tried and tested thread systems, R25, R28 and R32, have served underground drillers well for many years. However, with the introduction of ever-more powerful hydraulic rigs, these battle-worn solutions started to show weakness. Rod breakage at the bit end, either just behind the skirt or on the last thread, was becoming distressingly common. Why? Because it’s the most vulnerable part of the rod. Consequently, bits were lost, leading to costly downtime. Even worse, holes often had to be redrilled, reducing productivity. Putting it bluntly, drifting and rock bolting equipment was struggling to cope with the power of the new rigs. It was high time for fresh ideas. Extensive development by Atlas Copco Secoroc came up with the new Magnum SR range, which counters problems with breakage and offers performance to match that of the modern drill rig.

Thread of Innovation To solve the problem, Atlas Copco Secoroc faced two choices: either increase the dimensions of the rods and bits in the same way as everybody else, or find a new way. Being notoriously stubborn innovators, the choice was easy. During the creative process, three important insights emerged. First, the hole sizes should remain as for drilling with standard equipment. Second, the bits should be easy to uncouple. And third, the old thread design had to be left behind. As with all genuinely groundbreaking endeavours, the solution was deceptively simple. The secret of the Magnum SR thread design is that the ROCK & SOIL REINFORCEMENT

Magnum SR used in a bolting application.

diameter is larger at the end of the thread and smaller at its tip. By adding considerably more steel at the end of the thread, the new design was given a distinctive, conical shape. This concept not only upped the fatigue resistance of the rods, but also reduced the tendency to deviate during collaring. The Magnum SR thread design also has the added bonus that the bits are very easy to uncouple and change, saving time and equipment, and resulting in more holes drilled. Magnum SR has proved a big hit with operators.

The new Magnum SR system for drifting and rockbolting, specially designed for the new generation of powerful drillrigs, delivers more and straighter holes per shift and has a considerably longer service life than any competing system.

Field Tests Worldwide Extensive field tests with the Magnum SR were carried out on four continents, and involved more than a half million metres of drilling over a period of one year. 45

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products for hole diameters of 43-64 mm. The next addition to the family was the Magnum SR28 range. Tests have shown that SR28 is perfect for the rapid drilling of holes for rockbolts, but can also be used for small hole drifting. This new line replaces the traditional R25 system in 33-35 mm drilling. Tests in rockbolting have shown convincing increases in service life for both SR28 rods and bits. As with all other Magnum SR products, the bits are easy to uncouple, and as a result the drillstring is subjected to fewer damaging shockwaves, facilitating rapid changes and more holes drilled. All together, that means less downtime changing bits and rods, and more time spent drilling. Magnum SR35, together with Magnum SR28, are ultimately aimed at helping drillers advance their tunnel or drill rockbolt holes quicker than ever before. The most recent member of the family is SR32, which is specially designed for hole diameters of 38-41 mm.

Dawn of a New Era

Magnum SR bit ready to drill.

The system was put through its paces in mines, and in a variety of tunnelling projects. The results were unequivocal: service life and rig availability both enjoyed sharp increases. The tests showed that the Magnum SR systems increased service life by 25-100% on the rods, gave better service life of the bits, and created very high operator acceptance due to easy 46

uncoupling of the drillbits. This resulted in higher drilling productivity, thanks to easy collaring, straighter holes and better equipment availability during the drilling cycle.

Expanding Family The Magnum SR thread system was first introduced with the SR35, which has a comprehensive selection of

The trend in drifting and tunnelling is clear: the rounds are getting longer, and the rigs more powerful. Magnum SR was designed to withstand the high pressures so typical of today’s underground drilling operations. Although Magnum SR is relatively new to the market, the enthusiasm with which it has been received, and the performance that it delivers, have given an indication of the direction in which the product is heading. Atlas Copco Secoroc is genuinely confident that Magnum SR heralds the dawn of a new era in drifting and tunnelling, as well as for rockbolting. The success of this innovative system is beyond dispute. Drillers using it are not only drilling more and straighter holes than before, they’re also finding that Magnum SR lasts longer than any competing solution.

by Anders Arvidsson ROCK & SOIL REINFORCEMENT

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Rock Mechanics and Rock Reinforcement in Mining Behaviour of Rock Rock mechanics or geomechanics is a term often used to include all the steps that lead to define and control the behaviour of rock around excavations. From the geological and mechanical definitions, through rock mass characterization, to the design of reinforcement and calculation of factors of safety, rock mechanics provides the basis for the assessment of reinforcement needs.

Rock Mass Characterization Rock Mass classification and identification of failure modes

Shear analysis of critical structures

ROCK & SOIL REINFORCEMENT

Mechanical properties of rock masses

Calculation of “factor of safety”

Evaluation of zones of high stresses

Calculation of reinforcement needs

Calculation of reinforcement needs Influence of blast and dynamic events

Reinforcement design

Reinforcement design

Figure 1. (above) General process encompassed by the general definition of rock mechanics application to the design of structures in rock. Figure 2. (below) Simplified description of rock mass conditions and rock failure (from Hoek E., P.K. Kaiser and W.F. Bawden. 1995. Support of Underground Excavations in Hard Rock. Balkema p215).

Optimized Excavation Although rock mechanics is a relatively new science that deals with the mechanical behaviour of rock material, it

Low stress levels

Massive rock

intensely schistose. Massive rock will draw most of the intact rock strength, but will also accumulate load and can fail violently under the right conditions (see figure 3). Very fractured rock will tend to yield to stresses, and often deforms in a problematic manner (figure 4). Obviously, excavation shape, size and orientation also affect the response to the acting forces at play.

Jointed rock

In the context of definitions, it is often more accurate to talk about rock engineering, as components from geological, civil, mechanical and mining engineering are combined to create the process presented in figure 1. This global process can be very detailed, or quite basic, depending upon the magnitude of the mining operation and the available resources. The fundamentals include: the definition of the structural fabric of the rock mass including aspects such as joints, faults, shear zones; the evaluation of the mechanical parameters of the intact rock and structures; the identification and quantification of the failure modes based on stress and structural analysis; the influence of the excavation mode; and the design of the rock reinforcement itself. Differently formulated, it could be said that stresses and rock structures are the two most important factors affecting the stability of any excavation in natural strata material. Combination of various stresses regimes and fragmentation will dictate the behaviour of the excavation (see figure 2). Rock stresses intensity can vary from very low to very high, and intensity of fragmentation from massive rock to sugar cube structure or

Determination of in-situ stress

Evaluation of failure zones

Influence of blasting

Rock Engineering

Failure caused by overstressing

Structural failures and gravity

Heavily jointed block

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Massive rock subjected to low in situ stress levels. Linear elastic response with little or no rock failure.

Massive rock, with relatively few discontinuities, subjected to low in situ stress conditions. Blocks or wedges released by intersecting discontinuities, fall or slide due to gravity loading.

Heavily jointed rock subjected to low in situ stress conditions.The opening surface fails as a result of unravelling of small interlocking blocks and wedges. Failure can propagate a long way into the rock mass if it is not controlled.

High stress levels

Massive rock subjected to high in situ stress levels. Spalling, slabbing and crushing initiates at high stress concentration points on the boundary and propagates into the surrounding rock mass.

Massive rock, with relatively few discontinuities, subjected to high in situ stress conditions. Failure occurs as a result of sliding on discontinuity surfaces and also by crushing and splitting of rock blocks.

Heavily jointed rock subjected to high in situ stress conditions.The rock mass surrounding the opening fails by sliding on discontinuities and crushing of rock pieces. Floor heave and sidewall closure are typical results of this type of failure.

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This applies especially for the rock reinforcement and support aspects. Some rock reinforcement and support that can be perfect for static conditions may become quite inadequate when confronting seismic events or high stresses and deformations. It is then important to be able to predict future conditions, and use rock reinforcement that will still be adequate when conditions change, or will warn when in-situ conditions are close to exceeding the rating of the device.

Rock Reinforcement

Figure 3. Rubble created from a dynamic failure of a mine roof.

is now regularly used to optimize the performance of mining excavations in rock. Using rock mechanics leads to a better understanding of the behaviour of the rock masses, which in turn leads to a more effective and safer operation. Stress analysis is also more commonly performed on site, and results are easier to analyze thanks to the use of powerful desktop computers. The design process should also be repeated at later stages of the mining operation, as field conditions will almost always change for the worse. It is critical that the correct assessment of failure mode is made, as this understanding will lead to proper reinforcement instead of using a long and arduous trial and error methodology. As an example, when hard and massive rock fails, producing small fragments like those seen on figure 5, it is often a sign that the rock is overstressed and is rupturing in a brittle and uncontrolled way. This could be the precursor of seismic events and dynamic failure, which most rock reinforcement would be unable to control. It is also a fact that, as long as well-recognized brands of rock reinforcement are used, the support devices rarely fail as a result of poor material quality, but rather as a result of inadequate applications. 48

Numerical Modelling Long term excavation planning can benefit from detailed analysis like numerical modelling. Stress regimes can be predicted and mining sequences optimized to keep the stress level at a comfortable level: not too high to create seismic events, and not to low to create major structural instabilities. For day-to-day operation, numerical analysis will give results that must be confirmed by field observation, but can be used to plan with the right kind of conditions in mind. Figure 4. Ground conditions leading to yielding walls and roof.

Rock reinforcement devices and surface support are used to control the rock masses within a certain range, allowing safe and economical access to the excavated areas. Historically, before the 1900s, typical roof support in mines was timber posts and beam. Then, as early as 1905, roof bolts were reportedly used in coal mine roofs in the United States. In late 1920, systematic reinforcement of mine roofs was introduced to allow the use of mechanical full-revolving loading shovels, by providing room to manoeuvre free of conventional timber posts. Inclusion of channel irons, fastened by rock bolts to support large area of roof led to the principle of “suspension roof supports”. The need for early support to secure the lower roof layer to avoid

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100

Exceptionally poor

50

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large range of operational possibilities. Surface retaining supports like shotcrete and reinforcing membranes are now adding another dimension to the reinforcement of underground excavations, and their use in combination with rock bolts provides a counter-effect to stresses, water and time.

Figure 6. Estimated support categories based on the tunnelling quality index Q (after Grimstad and Barton, 1993).

Very poor

Poor

Fair

Good

Very good

Ext. good

Exc. good 20

2.3 m 2.5 m a 2.1 m d are te e r 1.7 m shotc 1.5 m ing in 1.3 m spac Bolt 1.2 m 1.0 m

10 7 5

20 (9)

(8)

(7)

(6)

(5)

(4)

5

(3)

(2) 4.0 m

0 15

m

m 0 12

m m

90

m

m

3.0 m

40

m 0m 25

m m

10

m

By 1979, J.J. Scott introduced the splitset rock bolt, and in 1980 Swellex bolts were introduced by Atlas Copco. These two products started the use of friction anchored rock bolts in underground excavation. During the 1980s, the cone bolt, a yielding rock bolt better adapted to rock burst events, was introduced in the South African mines, and its application in other continents is still under development. Around the same time, recognizing the need for support in moving ground, Atlas Copco introduced the Yielding Swellex. In 1997, Atlas

Extremely poor

Figure 5. Slabs created by the violent failure of a mine roof during a small rock burst.

m

Modern Rock Bolts

Copco introduced the EXL Swellex, an all around high performance yielding friction rock bolt. In 2003, Atlas Copco and MAI joined their efforts and introduced the Swellex Pm Line and the mechanized installation of SDA anchors. Today, Self Drilling Anchors that were first developed for ground engineering applications are slowly gaining ground as an alternative in extremely poor ground conditions. For long reaching reinforcement, cable bolts, coupled rebars and, more recently, connectable friction bolts (Swellex Connectable) and Self Drilling Anchors, provide a

50

loosening the upper layers, as well as the creation of roof beam action, laid the foundations of modern rock reinforcement principles. Around 1945, expansion shell anchors appeared in England, Holland and US, and by 1949 rock bolts began replacing timber supports in US mines at a rapid rate. By end of 1952, over 2 million rock bolts per month were being installed. In Canada, systematic bolting of roof in coal mines began in 1950. By the end of the 1950s rock bolts were in use everywhere, thanks to the systematic use of modern carbide tipped steels for fast hole drilling. Rapid installation, compared to timber sets, was also compatible with mechanized mining methods. Between 1952 and 1962 the introduction of grouted slot and wedge bolts, fully grouted untensioned deformed bars, as well as the hollow core groutable expansion shell rock bolt, provided a strong argument in favour of permanent reinforcement with rock bolting. During the 1960s, experiments were made with epoxy and polyester resins as bonding media. By 1972, prepackaged polyester resin systems were developed, tested and marketed. Immediately active, full-length reinforcement of rock masses became possible. Quality of installation remained an issue, and lengths of bars, as well as resin quality and setting times, created difficulties in installing the reinforcement system.

Span or height in m ESR

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d ete tcr ho ns u in ing ac sp

3

a are

24

2.0 m

1.5 m 2 1 1 0.001

1.3 m 1.0 m 0.004 0.01

lt Bo

0.04 1 0.4 10 4 Rock mass quality Q = RQD x Jr x Jw Jn Ja SRF

REINFORCEMENT CATEGORIES 1) Unsupported 2) Spot bolting 3) Systematic bolting 4) Systematic bolting with 40-100 mm unreiforced shotcrete 5) Fibre reinforced shotcrete, 50 - 90 mm, and bolting

10

40

1.5

100

400

1000

6) Fibre reinforced shotcrete, 90 - 120 mm, and bolting 7) Fibre reinforced shotcrete, 120 - 150 mm, and bolting 8) Fibre reinforced shotcrete, >150 mm, with reinforced ribs of shotcrete and bolting 9) Cast of concrete lining

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Adaptable Design

Conclusion

Rock reinforcement and rock mechanics applications are inter-related as the design of an excavation and its reinforcement is an implicit process in which most parameters are interdependent. The design of excavation also gets new “blood” with advances in technologies. Better long hole drilling equipment provides straighter boreholes that allow larger stopes with less development and better blasting control, and improvements in dilution and stability go hand in hand. However, recognizing that ground conditions are going to change brings the need for easily adaptable design methods of rock reinforcement. In this case, empirical methods can help rapid and sound decisions. Figure 6 presents a rock reinforcement design method based on the tunnelling index Q. Fast and reliable ground control practices can make the difference between a profitable extraction and a marginal one.

Rock mechanics in mining has evolved tremendously over the last 15 years with the availability of numerical models that run on desktop computers, and the very active transfer of knowledge and technology between research and mining operations. In fact, the practical application of rock mechanics in everyday mining is often considered a normal part of the extraction process. Rock mass classifications are used systematically in most mining operations in North America, and opening sizes and shapes are carefully designed and planned to fit both the equipment requirements and the stability limits. It is true that mining operations are often working at the limits of stability of excavations, but then the profitability of mining demands that knowledge and applications are at the forefront allowing the best overall performance . By developing local expertise and

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sharing it through conferences and publications, rock mechanics people are always pushing the limits of performance of excavations. In order to get the full benefit of rock mechanics application and rock reinforcement systems, the two must be linked and interconnected in a way to provide feedback information and data for each other. During the past two decades, the impact of accidents and damages has been better understood. It has been recognized that the safer the environment, the better the productivity and working relations. Social costs are now considered as valuable, and minimized. An objective of mining operations all over the world is to eliminate working injuries. As rock fall incidents are often fatal, they should be avoided by using integrated bolting systems to provide optimum reinforcement and support solutions.

by Francois Charette

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Performance of Swellex Rockbolts in Dynamic Loading Conditions Avoiding Dynamic Failure Dynamic failure of rock underground can generate high levels of kinetic energy and expulsion of rock from the opening surface. Rock material reaches velocities of a few metres per second and in those conditions, the rock reinforcement is more than often destroyed or at least mobilized in excess of its working range, resulting in caving or closed-in excavation contours. Rock reinforcement used in those conditions must be able to sustain the energy burst, as well as retaining the rock adequately before and after the event. In order to assess the Swellex capability in dynamic failure conditions, laboratory testing programmes have been undertaken to quantify the performance of Swellex rock bolts in dynamic loading conditions.

a

Testing Procedures The basic test procedure was: 1) turning on the electro-magnet and lifting the weight at the appropriate height above the impact position on the bolt; 2) initiating the datalogging system (when used) to measure impact load; 3) turning of the electro-magnet to release the moving weight; 4) if no failure, or complete sliding of bolt inside tube, the weight is hooked up again and lifted up for the next drop. The load data was Figure 1. Testing apparatus with a) original configuration and b) modified configuration for distributed impact, and c) completed test with modified configuration.

b

Testing Configuration Figure 1 shows the testing apparatus used to simulate the action of seismic events on Swellex rock bolts. All impact tests were performed on 2.1 mlong Swellex Mn12 bolts. The static weight of moving part was one metric tonne, or 1000 kg. In field failure, the Swellex bolts are usually broken at a distance varying from 10 cm to 50 cm from the head bushing. Failure of the bushing weld almost never occurs in the field. To try to reproduce the failure pattern observed in the field, the Swellex bolts were inflated in two steel tubes, with the top tube generating the anchorage. The second (see Figure 1) shorter, impact tube also generates some friction above the bushing and plate assembly, which dampens the impact. The rationale is that, since no bolts are breaking at the bushing weld in field events, it must be that the bulking occurs at such a ROCK & SOIL REINFORCEMENT

c distance from the head as to mobilize load from the anchorage and retaining force generated by the bushing-plate ensemble. The friction inside the steel tube was not sufficient to create failure of the bolt profile, and this highlighted the need to better simulate steel/rock anchorage capacity. However, this reduced friction demonstrated interesting behaviour that has led to a better understanding of anchorage requirements in dynamic loading. 51

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maximum dynamic strength differs from maximum static strength. A summary of impact testing is presented in Figure 2, including an impact test where the recording equipment was successful in picking up all of the information. Table 1 presents typical results from the laboratory testing programme.

A: Impact B: Sliding of bolt inside tube section C: Harmonic oscillation of weight after sliding has stopped.

A Load B

The typical measurements of the tests are: Impact load Sliding Load Final load on load cell (should be equal to the moving mass, i.e. 1 tonne) Time of sliding Time to failure (when it occurs)

C

Time

Analysis Of Energy Absorption Capacity Table 2 summarizes testing results on various types of rock reinforcement fixtures. Static steel properties can be used to preliminary assess the theoretical energy absorption capacity, but it has been found that load and deformation are different from static tests. Measurements show that the impact load exceeds the ultimate static tensile strength by a factor of about 1.5, while when shearing was observed (Figure 3), the impact load exceeded the ultimate shear strength, taken as 60% of tensile strength, by a factor of about 1.4. From the tests performed during the spring of 2004, the bolts showed only minimum yielding for loads exceeding

Swellex Sample A1

Load (tonnes)

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25 15 5 -5

0.95

1.05

1.15

1.25 time (s)

1.35

1.45

1.55

Figure 2. Typical signature of impact test on Swellex bolts: a) Typical phases of an impact test; b) actual impact test with sliding of bolt inside steel tube.

measured at time 0.00005 seconds.

intervals

of

Impact Tests Analysis Upon starting the test, the weight is elevated to a pre-determined height above the impact point. After being released, the weight accelerates until it reaches the impact point. At this point, the impact load is measured. Under the impact load, the bolt starts to deform, but almost simultaneously, it also starts to slide inside the steel tube. The sliding reduces the load on the bolt, so that it does not fail if it is not pinned or restrained. During sliding, frictional energy is dissipated according to the friction generated on the wall of the tube. As the weight slows down, the friction coefficient increases toward its static value, and the bolt is finally stopped. The momentum creates harmonic oscillations in the bolt, which acts as a stiff spring, and these are damped very rapidly. When the bolt is clamped or fixed so that it cannot start to slide at both ends, if the transmitted load at the restricted location does not reach the ultimate strength of the steel, the bolt only deforms elastically and plastically, 52

according to the load level. If the load reaches, or exceeds, the ultimate strength, then the bolt simply breaks. However, based on the test results, Table 1. Typical Impact Tests Results Result

Test 1

Test 2

Test 3

Test 4

Impact Load (T)

10.4

15.3

17.8

18.2

K(kJ)

9.1

8.6

6.1

9.1

Failed in shear

Failed in shear and tension

Failed in tension

Slided

Status of bolt

Table 2. Theoretical energy absorption capacity based on quasi-static load -strain properties Description

19 mm resin-grouted rebar 16 mm cable bolt 16 mm, 2 m long mech. Bolt 16 mm, 4 m debonded cable 16 mm grouted smooth bar Standard Swellex bolt Mn12 Swellex bolt Mn24 Swellex bolt Split Set bolt 16 mm cone bolt

Peak Load (kN)

Displacement (mm)

100 – 170 160 -240 70 – 120 160 – 240 70 – 130 105 – 110 120 – 125 220 – 240 50 – 100 90 - 150

10 – 30 20 – 40 20 – 50 30 – 50 50 – 100 25 – 35 45 – 100 80 – 120 80 – 200 100 - 200

Energy Absorption (kJ) 1–4 2–6 2–4 4–8 4 – 10 2–4 5.4 – 12.5 18 – 29 5 – 15 10 – 25

(Data from Kaiser, 1995)

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more than 50% of their maximum static strength. In fact, in dynamic testing, Swellex bolts elongated only 32 mm with a load of about 17 t on the test to failure, absorbing about 5.3 kJ of energy, which is similar to the energy absorption capacity calculated from static testing. When the rockbolt was not restrained, loading was not accompanied by failure. The energy that a rock bolt can accept is smaller when the bolt is pinned inside the tube (Figure 4), stretches to failure at the first blow. By contrast, when the bolt is able to slide slightly in order to avoid critical deformation, the impact energy that can be accommodated is quite a bit higher. The mechanical properties of the bolts’ components can give instructive insights on the energy absorption capability of a given bolt type. Table 2 gives some typical results from Kaiser (2, 3, 4) and from Noranda Technology Center (5). These results take in consideration only the elasticplastic behaviour of the shank/body of the bolts when submitted to a static load: the dynamic capacity is inferred in considering that the same loaddeformation relationship would exist during dynamic events. In Table 3, results from dynamic testing are presented and, from Ortlepp and Stacey (1), Swellex anchored in steel pipes could absorb 4 – 5 kJ of energy when sufficient anchorage is provided, or when the

Figure 3. Failure of Swellex bolt in shear.

sliding is restrained. Profile deformation during the tests ranged from 42 to 55 mm when the bolts broke. The impact was localized on the head only so the higher strength of the profile could not be mobilized. Results from Kaiser et al. (3) as well as from Ortlepp and Stacey (1), outline the fact that most reinforcement fixtures have limited capacities of absorbing energy when using deformation/yielding properties, and values range from 1 to 25 kJ of energy at most. However, when a reinforcement fixture dissipates

energy through sliding, its energy absorption capability is enhanced. Results from NTC’s tests on Swellex (2003) and Cone bolts (1998) show that, on a single event, it is possible to dissipate over 9 kJ with a Standard size Mn12 Swellex, which might be more with rougher tubes and longer bolts, and about 22 kJ with the Cone bolt tested at NTC (Kaiser). These values exceed by far any strain energy accumulation mechanism. It is important to understand that, in dynamic loading, ultimate load and deformation are not the same as in

Figure 4. Failure of bolt at pin location.

Table 3. Energy absorption capacity from dynamic testing

Bolt Type

Source

Single Event

Cone Bolt (NTC) from Kaiser and al.

Kaiser and al.

Variable with Max: 22 kJ

Swellex

Ortlepp and Stacey

4.1 – 5.1 kJ

Rebars

Ortlepp and Stacey

4.1 – 5.5 kJ

Swellex Mn12 2.1 m

Atlas Copco/ NTC

9 kJ

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static loading, but the deformational energy absorption seems to be quite similar. Tests results from NTC and Atlas Copco also demonstrated another important fact. This is that maximum energy can be absorbed when the friction properties are tightly matched to the strength of the material. When this right combination is reached, the bolt head will move just before the shank/bolt body enters the deformation phase. This allows maximum energy absorption without failure of the unit, and provides a consistent energy absorption capacity, coupled with stable static load bearing capacity, equivalent to the rated capacity of the bolt.

Conclusion Dynamic testing at the laboratory has shown that Swellex bolts can accept and dissipate a reasonable amount of energy without failing, and still provide an adequate load capacity, as long as the anchorage length is adequately

54

coupled to the static anchorage capacity. This operation was successful with steel tubes instead of rock. The next step is to increase the friction against the bolt in order to simulate an anchorage capacity of 130 to 180 k/m, and repeat the same testing with Mn24 bolts. It is also very interesting to consider what kind of energy dissipation could be achieved when using an Mn24 instead of an Mn12 bolt. As the bolt itself is twice as strong, the maximum load could be doubled, and, since the friction could be adjusted in order to provide the right anchorage capacity, the energy absorption could certainly be in the order of +18 kJ per event. The conclusions obtained from these laboratory tests is being applied to the Hybrid Swellex bolt that combines the controllable sliding ability of the Swellex with the strength and reliability of MAI bars.

References 1. Charette, F. Performance of Swellex rock bolts under dynamic loading conditions, The South African Institute of Mining and Metallurgy. Second International Seminar on Deep and High Stress Mining, Johannesburg 2004. 2. Ortlepp, W.D., Stacey, T.R. Testing of tunnel support: Dynamic load testing of rock bolt elements to provide data for safer support design (GAP423), June 1998. 3. Kaiser, Canadian Rockburst Design Handbook, 1995. 4. Kaiser et al, Drift Support in burst-prone ground, CIM Bulletin, March 1996. 5. Kaiser, Support Against Rock Burst – Short Course 1995–2003. 6. Falmagne, V. Etude de faisabilité: tests d’impact sur Swellex. Centre Technologie Noranda, Mai 2003.

by François Charette

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Slope Stabilization with Self Drilling Anchors Soil Nailing for Reinforcement Soil nailing is used to reinforce and strengthen ground which has questionable stability. Soil is generally a poor structural material because it is weak in tension. Steel, on the other hand, is strong in tension. The fundamental concept of soil nailing is to effectively reinforce soil by installing closely spaced grouted steel bars into a slope or excavation, as construction proceeds from the top down. A soil nail is therefore commonly referred to as a “passive” anchoring system, meaning that it is not pre-tensioned, as is normal with ground anchors. Unstable slopes or excavations consist mostly of unconsolidated soils or deteriorated rock formations. To install conventional soil nails, a cased borehole drilling method is required to overcome such difficult and unstable ground conditions. An alternative is the MAI Self Drilling Anchors (MAI SDA), which is specially designed for use in ground where the boreholes tend to collapse during the drilling process if casings are not used.

Advantages of Self Drilling Anchors Since the slow cased borehole drilling methods were superceded, the speed of installation has increased considerably, up to 20-30 soil nails/day using MAI SDA, and the risk of re-drilling time spent cleaning collapsed boreholes has been eliminated. The selection of the drilling equipment for MAI SDA installation is also more flexible, especially for working in confined space. MAI SDA rods are manufactured with a continuous ISO standard ROCK & SOIL REINFORCEMENT

Installation of SDA R38 N with ROC D7 at Carriere d’Arvel, Switzerland.

thread, affording the flexibility to adjust the nail to the actual requirements on site, without waste or delay, as construction proceeds. Transportation and handling of MAI SDA to and on site is safe and economical, because of the commonly used rod length of 3 m or 4 m. These can be extended using couplings to allow installation of soil nails up to 15 m depth, depending on the geology. There is also the option to use simultaneous drilling and grouting installation techniques.

Method of Installation Self Drilling Anchors are installed with air driven or hydraulic rotary percussion drilling equipment, using a borehole flush medium suitable for the specific ground conditions. There are three types of borehole flush: water flush for long boreholes in dense to very dense sand, gravel formation or rock conditions, for a better transportation of large cuttings and cooling of the drill bit; air flush for short boreholes in soft soil such as chalk and 55

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Galvanized MAI-SDA R 25 and R32 anchors installed into loose and collapsing ground using simultaneous drill and grout at the Shortlands Junction, Bromley, Kent, UK.

clay, where water spillage is to be avoided; and simultaneous drilling and grouting (SDG) for all lengths of boreholes in all unconsolidated soil conditions. Using SDG, the grout stabilizes the borehole during installation, providing Principle of the MAI Self Drilling Anchor.

a better grout cover along the nail shaft. The grout has good penetration into the surrounding soil, so higher external friction values are reached, and the installation is completed in a single drilling operation, saving time. By utilizing a sacrificial drillbit, the MAI SDA is drilled continuously forward without extraction, until the design depth is reached. To reach a required nail length of 12-15 m, the 3 to 4 m standard rod lengths are easily coupled together.

When using the first two flushing media for the drilling operation, the soil/steel interface has to be created by grouting through the hollow stem of the anchor. The grout exits through the flush holes of the drillbit, and backfills the annulus around the nail that has been cut by the larger diameter of the drillbit. For the third operation, the flushing medium is already a grout mix, which has the ability to harden after the installation process is completed. A typical application of SDA is currently being carried out by the open cast mine Carriere d’Arvel in Switzerland. Here an Atlas Copco ROC D7 drillrig equipped with a Ceminject (integrated rotary injection) adapter and a rod handling system is being used for SDA installation. The ROC D7 feed reaches to a height of 7 m, allowing installation of two rows of SDA from one position. The rod handling system contains at least two sets of three 3.5 m-long R 38 N SDA rods, facilitating installation of two complete 10 m-long Soil Nails without having to manually feed

ROC D7 offers excellent reach with a folding boom.

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Atlas Copco ROC D7 installing MAI SDA for soil reinforcement using MAIm400NT grout pump.

extension rods at these extreme working heights. The newly developed integrated injection adapter (Ceminject) can be used for either simultaneous drilling and grouting, or as in this case, first drilling to full depth with an air flush and then grouting the annulus of the borehole. The SDA installation becomes a fast continuous mechanized process with high grouting quality in a safe working environment. Similar methods were used to stabilize the slope at Shortlands Junction, Bromley, Kent, UK, where loose and collapsing ground was affecting operation of the railway.

Installation Using ROC Drillrigs The use of self drilling anchors for stabilization and reinforcement work in soft rock is common both in the underground world of mines and tunnels and, for a wide variety of applications on the surface. On surface, it is generally poor quality ground and soil that threaten the stability of installations or landscapes. Embankments along roads and railways, various types of foundations and hills prone to landslide, and the sidewalls of cut-and-cover tunnelling are just a few examples. Field tests have shown that the Atlas Copco ROC D-series of drillrigs can be used to install self-drilling anchors (SDAs), as well as for blasthole drilling. Hence, contractors who own one of these crawler rigs for quarrying operations are perfectlyequipped to take on stabilization jobs. ROCK & SOIL REINFORCEMENT

A simple conversion kit enables this rig to be converted to an SDA installation unit, without losing the advantages of the ROC D7 standard, high-tech features. The rock drill is fitted with a kit consisting of an Ceminject (integrated rotation injection) adapter, swivel and brackets to replace the standard shank adapter. The SDA shank adapter is a female shank having integrated coupling sleeve to ease uncoupling. Available for R32 and R38 anchors, it requires a flushing head with inner diameter of 53 mm, normally used on surface crawlers, because of the size of the female front part of the shank adapter. Ceminject is a SDA shank adapter combined with a separate swivel providing flushing media and grout. The swivel is mounted on the rock drill with a bracket and has two separate inlets. The Shank Connector is a coupling sleeve locked to the shank adapter. To provide the locking function a special male T38 shank is required. This is an alternative to SDA-shank, when installing R51 or T76 anchors and when alternation between bolting and blast hole drilling is required. A flushing head with inner diameter of 53 mm is needed. The Rod Handling System RHS 52 is used for carrying bolts on surface crawlers. The system is equipped with SDA bushing halves in the gripping arms and the star wheels carrying the rods. BSH 110 is a hydraulic drill steel support providing gripping and guiding function. To drill SDA it is equipped with the rubber bushing and steel bushing halves to match the anchor size.

The grout pump m400NT, available from Atlas Copco MAI, is also recommended.

Two-man Operation Only two people are needed – one to handle the drilling, and one to handle the pump. The SDAs, with their R threads and sacrificial bits, are installed and grouted in one operation. These easy adjustments will enable ROC D7 owners to get the best, and the most, out of their equipment. For some, it may open up whole new markets that they have previously not even considered. The beauty of being able to adapt the ROC D7 for such applications is that the contractor can make full use of the rig’s powerful and flexible hydraulic system. The folding boom, for example, can be positioned up to a height of 7 m beside a slope, or very low for horizontal toe-hole drilling. It can also be positioned at extreme angles, enabling SDAs to be used in very inaccessible places.

Connecting Grout Pump and Ceminject adapter Most of the time there is a need to alternate between flushing with water and grout. In surface SDA installation, it may be inconvenient to grout during drilling, as this may contaminate the feed with the grout, or minimize spillage during collaring. The alternative is to flush with water when drilling-in the anchor, and then grout it through the Ceminject. This would be the final step in the installation sequence, prior to uncoupling the last rod from the rock drill. To alternate between water and grout, connect the grout pump and water hose to a y-coupling equipped with two valves, so that water or grout may be selected. The hose from the y-coupling is then connected to the Ceminject, either direct or by letting it run on the feed through the hose tree and over the hose drum. This type of y-coupling requires manual switching between water and grout. When installing SDAs using a surface drillrig, some contractors have 57

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pump and the other to the water flushing system on the rig. The water supply hose should be equipped with a nonreturn valve at the connection to the Ceminject, in order to prevent grout from entering the water system. The two hoses can be put on the feed over the hose drum. This system makes it easier to control both water and grout flushing, with the water controlled by a valve on the rig, and grout flow by starting and stopping the pump. The grout pump can be controlled remotely by the rig operator, or by the pump operator on demand from the rig.

COP 1832 rock drill with Ceminject adapter.

SDA Installation Cycle

Standard rod handling magazine with SDAs and couplings.

The special bushing halves prepared for firm gripping of the SDAs.

chosen to drill and grout simultaneously, using only grout as the flushing medium. This has the advantage that, once the anchor is completely drilled into the ground, it is fully grouted and ready to be attached to the face plate. This makes the connection between the grout pump and the Ceminject straightforward, needing 58

only a single hose. It is possible to replace the hose for air flushing by the grout hose by attaching it to the hose tree and letting it run over the hose drum to the rock drill. To simplify the system further, and to reduce number of people needed to do the installation, two hoses can be connected to the Ceminject, one to the grout

The optimal SDA installation cycle comprises the following steps: 1. Drill first SDA rod, either with simultaneous drilling and grouting or with conventional air or water flush, guiding with the Drill Steel Support (DSS) in open position. When the rod has fully penetrated into the soil/rock, stop the flush and loosen the rod end connection to the drifter by clamping the DSS and unscrewing the female shank adapter. Uncouple before retracting the rock drill. 2. Extend with next rod using the rod handling system, open DSS and commence flushing, then resume drilling. 4. Repeat rod-adding sequence until final design length of the anchor has been drilled. 5. If simultaneous drilling and grouting modus has been used, then the installation cycle is now complete and the feed can move to the next anchor position. 6. In air- or water-flush modus, switch over to grouting mode and, while maintaining a slow rotation of the anchor, commence grouting until the hole is full. The in-situ rotation mixing process of the grout guarantees a homogeneous filling of the annulus, improving corrosion protection and external friction values of the rock–grout interface. 7. The installation cycle is completed and the feed can move to the next anchor position.

by Mark Bernthaler ROCK & SOIL REINFORCEMENT

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3D Images for the Design of Rock Support Reducing Rock Fall Hazards in Tunnels Rock blocks falling from the roof or sliding into the tunnel can be a hazard for the miners and equipment, besides generating additional costs. Efficient identification of potentially unstable blocks and instant design of appropriate rock reinforcement thus contributes to safer and more economical tunnel construction. A recently developed imaging system and evaluation software assists in identifying unstable blocks and design of rock support.

Introduction Currently the assessment of potential for excessive overbreak and discontinuity controlled block falls or slides heavily relies on experience. Measurement of discontinuity pattern and orientations is done manually, if at all. The evaluation of the incomplete and inaccurate data with respect to block fall hazard is slow, and usually does not allow for the determination of appropriate rock support in time. In order to master these shortcomings with respect to efficiency and accuracy, a 3D imaging system has been developed consisting of an imaging device and 3D evaluation software components. Named the JointMetriX3D® system, it unites several features: • Data (image) recording at the face • 3D image generation and assessment • Metric and accurate measurement of discontinuity orientations, distances, persistence, and other geometrical properties • Link to other applications, such as CAD ROCK & SOIL REINFORCEMENT

Evaluated 3D image generated with JointMetriX3D®. Joints are represented by traces and areas. The arrows indicate the orientation of an area by its normal vector while the spherical triangles indicate the orientation of the plane fitted through the trace. The absolute position and orientation of the joints is directly determined.

A 3D image combines a large number of three-dimensional surface measurements with a high-resolution colour image, thus easing visual inspection of the rock mass.

Imaging at the Tunnel Site The major goal is to record the actual rock mass conditions comprehensively by producing images that allow reproducible assessments. The stereo-photogrammetric principle of JointMetriX3D® requires two images of the same area captured from different positions in order to obtain 3D information. Currently, two options for imaging are available. The first one uses conventional calibrated single lens reflex (SLR) cameras, while the other uses a panoramic line scanner.

SLR Camera A conventional SLR camera with a minimum 6 MPix sensor is used to

take two free positioned images. In order to allow for measurements, the camera is calibrated. Scale and local orientation is introduced by locating a vertically levelled bar somewhere within the region of the images. The whole data acquisition process requires only about one minute. Processing the images leads to 6 MPix 3D images with several hundred thousand 3D measurements.

Panoramic Line Scanner For very high-resolution images, the panoramic line scanner should be applied. This scanner is capable of producing images of more than 100 Mpix, recording very fine details. During scanning, the device head rotates, recording the face column by column. A major advantage of the panoramic principle is that existing reflective targets in the tunnel can be used to establish a reference of the image to the tunnel. Data acquisition 59

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on site typically takes in the region of ten minutes, leading to 3D images which are referenced to the tunnel coordinates.

3D Image Generation and Measurements From a stereoscopic image pair a 3D image is reconstructed by purposebuilt software. This can be carried out by personnel on-site or off-site, using secure Internet connections. Once a 3D image is ready, assessments and measurements are taken from it using the 3D software JMX Analyst. This software allows the inspection of 3D images thoroughly, giving a realistic impression of the actual conditions. Measurements are taken directly on the 3D image using the software, such as: • Joint locations, orientations, spacing, persistence, etc. • Lithological boundaries • Areas • Volume of overbreak JMX Analyst contains a tool to plot joint data in stereographic projection and the variation of orientations of joint sets (cone of confidence, spherical aperture, etc).

All measurements are metric and referenced either to a relative or the tunnel coordinate system, and can be exported directly into standard file formats. A free copy of JMX Analyst is available for download at www.jointmetrix.com/.

Prediction of Block Failure Modes and Support Design The measurements derived from 3D images are used to establish a consistent and accurate ground model. Using the acquired information on the rock mass structure, potentially unstable blocks are identified with respect to their location, volume, and weight. Once the failure mode and the properties of the blocks are identified, the quantity, location and length of required bolts to stabilize the blocks is determined. Further processing of the existing data can be used to extrapolate the rock mass structure in a representative volume around the tunnel, allowing an assessment of the conditions ahead of the face. This enhances the quality of short-term prediction, thus reducing any surprises during excavation.

An imaging system, such as JointMetriX3D® can be installed on a drilling jumbo, allowing for an instant imaging during work. Recorded data are transferred to the office for evaluation, and the necessary information for the rock reinforcement transferred back to the drilling equipment within minutes.

by Wulf Schubert, Markus Pötsch and Andreas Gaich 3D imaging with SLR camera.

Rock block support by bolting during tunnel excavation . Prediction and final design is based on the rock mass structure derived from JointMetriX3D® measurements.

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Introducing Swellex Hybrid New Versatile Rock Support By combining the benefits of Swellex bolts with those of the MAI Self Drilling Anchors (SDA) system, Atlas Copco has developed a new versatile type of rock support that can be pre-tensioned, grouted or use as a rock reinforcement system for seismicity. The new Swellex Hybrid provides immediate support, long life expectancy and the level of safety and productivity characterizing Atlas Copco Rock Reinforcement products. By coupling MAI SDA bolt sections, the system can be installed in very tight locations to virtually any hole length.

Competence Centre The Atlas Copco Competence Centre team was looking for a type of rock bolt offering the following features: immediate and efficient support; immediate anchorage in any type of rock; adaptable to any hole lengths; fast and trouble-free installation; longevity when required; pre-tensioning capacity when requested; and the possibility to control the anchorage capacity and behaviour of the rock support to maintain the bolt integrity in case of seismicity. Shortly after Atlas Copco acquired the reputable MAI SDA system, it Hybrid bolt for long anchorage in rock.

ROCK & SOIL REINFORCEMENT

became apparent that the solution was to combine the two. Equipped with a Swellex end, the new rock bolt offers immediate anchorage. As only a short segment of Swellex is required, the product may be installed in long holes by simply adding new MAI SDA segments. Good anchorage capacity in any type of rock is another advantage of using a Swellex segment at the end of the bolt. Furthermore, as a plate and nut are fastened on the MAI rod side, real pretensioning is possible. A special coupling has been developed to connect the MAI rods and the Swellex segment for the purpose of grouting, offering longevity while adding stiffness in shearing. By limiting the length of the Swellex segment, the anchorage strength can be controlled. Sliding behaviour at high tensile load consumes energy without compromising the integrity of the bolt, with the insurance of a perfect, low-cost installation every time.

Pre-tensioning and Grouting The vast majority of grouted rebars and cable bolts are not pre-tensioned, mainly because this process is cumbersome and time consuming. The need for pre-tensioning is higher if ground movement is likely to occur during the cement curing period. As pre-tensioning creates an active support, larger stress can be absorbed without rock failure. The Swellex segment and the grouting device are inserted first, followed by as many MAI SDA rods as needed to reach the required length. The Swellex segment can then be inflated through the MAI SDA anchors. A plate and nut are installed after inflation to provide immediate support and real pre-tensioning. Grouting can then be carried out immediately, or later, once equilibrium has been reached with no further movement of the rock mass expected.

Components 1 Retainer 1-

22 Swellex Connectable (blind segment)*

3 Grouting valve* 3-

4 MAI Anchor Rod R32 4(hollow bar)

55 MAI Anchor Coupling

66 MAI Anchor Rod R32

77 Face Plate 8

8- Nut

99- MAI Anchor Adaptors

for Swellex inflation and grouting * Notes The Grouting valve(3) is included with the special version of Swellex Connectable(2) when Hybrid bolt is to be grouted. - A standard Swellex Connectable blind segment (2) is used when the hybrid is to be used for energy absorbancy.

Installation sequence of Swellex Hybrid for pre-tensioning and grouting.

The grout then achieves strength and resistance.

higher

Seismicity Most of the present generation of rock bolts, such as cone bolts and durabar, that address the seismicity problem

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use the same principle of having a part of the system that can disengage and absorb energy through friction or deformation. The efficiency of these systems depends on the quality of the installation, which varies significantly with the quality of grout and de-bonding agent, rock mass condition, and experience and training. Often, because of poor quality of installation, these systems have not achieved the expected success and efficiency underground. The advantage with the Hybrid system is that, once the anchorage capacity (kN/m) is deduced from onsite pull test of the short Swellex segment, it is easy to calculate the length of the Swellex required to reach the maximum sliding strength that would not damage the bolt under dynamic conditions, and the free sliding length needed to dissipate the energy. The installation is easy and, above all, always perfect, as it is controlled by the Swellex pump. The installed system can also be tested at any time to make sure it is working according to calculation.

Site Testing The Hybrid bolt is now being tested at WASM facility in Australia to determine the optimal anchorage for maximal energy absorbancy of the system under dynamic loading conditions. Both the Hybrid bolt and its system of controlled energy absorbancy are patented. If, for example, a 1 m Swellex Pm24C offering a 150 kN anchorage is proven to slide (yielding strength = 200 kN) under dynamic conditions without damaging the bolt, a sliding of 0.15 m would consume as much as 22.5 kJ of energy. Once sliding behaviour is tested and the system proven, a sliding pull test (on a short bolt segment inflated) performed on site will confirm the anchorage capacity. The length of the Swellex will then be chosen to match the maximum sliding strength, and sliding distance calculated according to the energy to be dissipated. This system offers the facility to be tested at any time. Recent studies have shown that the quality of surface support is of paramount importance for ensuring the 62

efficiency of rock reinforcement for seismicity, in order to make the system absorb the energy and preserve the rock mass between each bolt.

Life Expectancy When it comes to protecting the investment, for long life expectancy Swellex Hybrid offers solutions to match the threat. When used for pre-tensioning and grouting: Atlas Copco has developed a special grouting device that is coupled between the Swellex segment and MAI rods. This allows the Swellex Hybrid to be inflated, pre-tensioned when required, and then grouted through the MAI SDA rods. The grout then protects the Hybrid bolt, preserving the MAI rods from contact with the environment. For full protection from a corrosive environment, or for long life expectancy, MAI rods can be supplied galvanized, and Swellex in Plasticoated or coated versions. The grout will then offer the first protection layer, followed by the zinc layer, or the plasticoating on the Swellex. As the MAI bolts are grouted from inside out, there is no access for corrosive elements. Installation sequence of the Atlas Copco Swellex Hybrid.

When used for seismicity, Swellex plasticoated and galvanized MAI SDA anchors are recommended for corrosion protection. A plug can be used to protect the inside of the Swellex in the long term.

Installation Sequence For pre-tensioning and grouting: 1-Drill the hole to the required length using 48 to 51 mm bit. 2-Insert Swellex (the length can be determined from pull test – should be sufficiently long to generate pull out resistance equal or higher to its yielding strength into the hole). 3-Thread the SDA rod all the way into the grouting valve on the Swellex. Extend with additional SDA rods and special Hybrid couplings (good for 300 bar) to match the hole depth. 4- Install plate and nut 5-Attach inflation coupling to the last SDA rod. 6-Inflate Swellex through the SDA rods using a standard Swellex pump having 300 bars in water pressure. 7-Open the grout valve (in the Grouting device) by rotating the MAI rods by a 1/2 turn anti-clockwise. 8-Detach the inflation coupling. 9-Pre-tension the bolt. 10-Grout (MAI 400 NT Grout Pump is recommended). For seismicity: 1-Drill the hole to the required length using 48 to 51mm bit. 2-Insert Swellex (the length can be determined from pull test – should be sufficiently short to generate pull out resistance lower to its yielding strength into the hole). 3-Thread the SDA rod to the Swellex. 4-Install plate and nut. 5-Attach inflation coupling to the last SDA rod 6-Inflate Swellex through the SDA rod using a standard Swellex pump having 300 bars in water pressure. 7-Detach the inflation coupling. 8-Pre-tension the bolt. By combining the merits of the Swellex and MAI SDA systems, Atlas Copco has invented a completely new approach to rock bolting.

by Mario Bureau ROCK & SOIL REINFORCEMENT

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Swellex in Mining Safe and Speedy Support Rock support is often a bottleneck in the business of underground mining, and an obvious solution is faster rockbolting. The cost is negligible when compared to the higher profits that can be made by keeping equipment fully and economically employed to increase production. The mining industry is increasingly recognizing that Atlas Copco Swellex rockbolts, which are quickly and safely installed to give immediate support, are speeding up operations and boosting revenues. Over the past two decades, the Swellex rockbolting system has become world famous as the simplest, fastest and most reliable ground reinforcement technology available. The Swellex bolt is a folded steel tube, which is inserted into a predrilled hole in the rock. Water is blasted into the tube at high pressure, blowing out the fold and expanding the tube into the exact shape of the hole, adapting to every irregularity. Bolt installation takes less than 30 seconds, and provides full and immediate support along the entire hole length, in ground conditions ranging from the hardest rock to clay and even non-cohesive material. The system speeds up rock reinforcement considerably and, over the years, has built up an enviable reputation for saving time and money, as well as providing a safer underground environment for miners and tunnellers alike. In the tunnelling business, Swellex bolts are already accepted as the key to better operational efficiency. Now they are ensuring higher advance rates, productivity and quicker access to orebodies in mines as well.

Forward Stabilization Using Swellex In single-face development, high-speed rockbolting obviously cuts the time to completion. But in multiple face development or ore extraction, the objective is to utilize manpower and equipment efficiently, as well as to advance the faces on ROCK & SOIL REINFORCEMENT

schedule. This means that operations must be synchronized so that one does not fall behind, holding up the others and wasting time and money. The development of Atlas Copco’s Rocket Boomer and Boltec rigs is constantly reducing drilling time, making Swellex the perfect partner to provide reinforcement quickly, so that the next operation can start without delay. Drilling ahead of the tunnel face to install bolts or grout as pre-reinforcement, is a common way of improving the rock quality before excavation takes place. Instead of relying on supporting the ground following excavation, pre-reinforcement increases rock strength prior to excavation. There are several benefits to this. First, a pre-reinforced rock mass will be less damaged, both by blasting and by the elastic and non-elastic stress redistribution of the excavation process. Second, the rock mass is never without support, even at the split second following blasting of the round. Third, the support can be more active when installed early, rather than passive when installed later. Fourth, pre-reinforced ground will not deteriorate or collapse as rapidly as a totally unsupported excavation, allowing a safe working period for installation of regular support. The Bieniawski diagram shows the relationship between the unsupported span and stand-up time of an excavation with reference to its rock mass quality. Empirical observations have shown that, for a given

Bieniawski diagram showing stand-up times for different spans and rock classes.

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excavation size, a linear reduction in Rock Mass Rating (Bieniawski, 1974) will lead to a logarithmic reduction in unsupported stand-up time. Hence, a linear increase in excavation span results in a logarithmic increase in instability potential. For large span drifts, the time period available to install roof support is significantly lower than for small drifts. In the case of a 4.3 mspan tunnel driven through poor to very poor quality rock, it may be logistically impossible to support the roof before it collapses. Obviously, the operational and safety implications of such cases are important. Field observations show that cable bolts installed in stopes before the first blocks are blasted are more effective than cable bolts installed after the slot or cut has been excavated. For cable bolts installed prior to stope exploitation, the grout curing period is generally respected. This is not always the case for cable bolts installed during

Project: Underground gold mine pre-reinforcement. Location: Mine Doyon, Rouyn-Noranda, Quebec. Mining method: Longhole stoping with cemented rock fill. Rock: Quartz and sulphide veins surrounded by seritic schist. Rock reinforcement required: Protective umbrella in access drift. Rockbolt selected: Super Swellex.

Mine Doyon Experience A variation of the umbrella method was attempted at Mine Doyon, located near Rouyn-Noranda, in northwestern Quebec. The Mine Doyon property is one of the most important gold-bearing orebodies in production in Canada. At least four major ore zones are found on the Doyon property. Economic mineralization is found on a corridor that extends at least 2 km E-W, and from surface reaches a depth of over 1,000 m. The No.1 Ore Zone is defined by a major quartz and sulphide vein system, oriented E-W. The orebody is also oriented E-W, dips steeply south, and has an average width of 8 m at depth. It is surrounded by sericitic schist corresponding to the sub-unit 4b of the Blake River Group (Savoie et al, 1991). Mining method is long hole stoping, with cemented rock fill. Mill production is around 3,500 t/day. Several tectonic events have been identified, among them a N-S compression 64

stope exploitation, when production concerns may override ground support design concerns. The cohesive effect of the cable is greater when added to undisturbed ground than when added to weakened and disturbed ground. In tunnelling, the umbrella grouting method of pre-reinforcement is frequently used. This method pre-supports the planned roof area with steel rods. Large holes are drilled in the future roof perimeter, and grouted at high pressure with high strength, fine grained cement grout. Through each cemented hole, a smaller hole is then drilled, in which a highstrength reinforcement bar is grouted. Although highly effective for shallow tunnels driven in very adverse ground conditions, it is easy to see that such a work-intensive operation would be deemed neither practical nor economic for mining applications, although the underlying concept could definitely be useful.

followed by a N-S extension; an inverse shearing caused by a NW-SE compression; and a polyphased fracturing caused by an as-yet undetermined stress gradient. The footwall of the No. 1 Zone is located in very poor quality sericitic schist, with Rock Mass Rating values between 0 and 30. This alteration zone runs for about 100 m up to the ore body, which is located in very weak chloritic schists. Stope development in this ore zone was delayed due to repetitive caving in access drifts. The rock mechanics engineer at Mine Doyon designed a pre-reinforcement method using cable bolts installed over the future roof of the access drifts. An array of nine 50 ft cable bolts was used to presupport the roof during drift development. The method was successful from a rock mechanics point of view, allowing three to four rounds to be taken before installing heavy support consisting of vertical cable bolts and shotcrete. Primary support could be installed during the normal cycle without safety problems. Although stability was achieved, productivity was compromised, since the bolter was tied up in stope preparation and rehabilitation work. Also, since several levels were being developed concurrently, travel time for the equipment and cable grouting crew was significant. A better solution was needed. ROCK & SOIL REINFORCEMENT

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Requirements were: easy integration in the normal development cycle; installation before the next drift advance; effective support; and reasonable cost. In order to increase productivity and regain some flexibility, it was decided to try pre-reinforcement using Super Swellex bolts instead of cables, and to slightly reduce drifting length to about 3 m. Five to six Super Swellex, parallel and spaced 60 to 75 cm apart, are installed sub-horizontally over the perimeter holes. Holes are drilled using the development drillrig. Prereinforcement holes are 50 to 60 cm longer than drifting length, to accommodate the 3.6 m-long bolts. Inflation pressure is 300 bars. Several variations of the method were used to secure pillars and cuts in stopes. With the Super Swellex bolts, productivity actually increased to the same level as for ramp and drift development in fair to good quality rock. Since the few extra holes required for the spiling bolts are drilled at the same time as the blasting holes, and the bolts are installed in the short period between drilling and loading, this pre-reinforcement method does not increase the excavation cycle time. The experience was a total success, and the method became a standard at Mine Doyon for bad ground conditions. Presently, around 300 m of access drift and

Detailed Research in Peru The Ares Gold and Silver Mine is located 275 km north-west of Arequipa, Peru, nearly 5,000 m above sea level. It is a new ore deposit in which the Victoria vein, nearly 2,000 m long and up to 200 m deep, is the main mineralized structure. The design of drift support in the mine has been the subject of detailed research by its soil mechanics team, and different types of bolts were field-tested. The final choice, for both permanent and temporary support in the five different types of rock at the mine, was Swellex bolts from Atlas Copco. Super Swellex and Midi Swellex bolts are being used in areas where the metal content is high and recovery must be around 95% and, in addition, some 1,600 Standard Swellex bolts/month are being installed at the mine. Thanks to its special features, the Swellex system has not only increased safety, but has contributed to an increased advance rate and improved economy. ROCK & SOIL REINFORCEMENT

stope have been developed using this method. Close cooperation between the engineering and production departments made this success possible.

Pre-reinforcement using Super Swellex at Mine Doyon, Canada.

Project: Underground gold and silver mine. Location: North-west of Arequipa, Peru. Excavation method: Drifting. Rock: Variety of different rocks. Rock reinforcement required: Permanent and temporary support. Rockbolt selected: Standard, Midi and Super Swellex.

Installing Swellex at Ares mine.

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Super Swellex aids safe and cost effective development at Louvicourt mine in Canada.

Project: Mine with copper, zinc, silver and gold. Location: Near Val d’Or, Quebec. Mining method: Longhole stoping with paste backfilling. Rock: Volcanogenic massive sulphide deposit. Rock reinforcement required: Support through fault zones. Rockbolt selected: Super Swellex.

Louvicourt Solution The Louvicourt Mine is a polymetallic orebody of copper, zinc, silver and gold, 25 km east of Val d’Or in northwestern Quebec. It is a volcanogenic massive sulphide deposit, starting 47.5 m below ground surface. It is part of the Abitibi Greenstone Belt, within the Precambrian Shield of eastern Canada. The orebody dips 70 degrees north and strikes E-N-E 66

with a plunge to the east. Dimensions of the orebody are 300 m along strike and 500 m along dip. Thickness varies from 20 m to 100 m. The mining method is long hole stoping with paste backfilling. Systematic stability problems are encountered while drifting through fault zones disseminated in the orebody. The gouge associated with the faults, the unfavourable dip of the two main joint sets, and the intense black chlorite alteration of the joints, contribute to the formation of high roof and unstable ground conditions. Gouge thickness can reach up to 90 cm. An efficient solution to this problem has been to use Super Swellex bolts as a prereinforcement method. Three to four rings of 3.6 m-long Super Swellex, on a 1.5 m x 1.5 m to 2.0 m x 2.0 m pattern, are installed in the roof of the drift before the next advance in the fault zone. The holes are drilled 50 degrees upward, and the bolts are inflated to 300 bars using a pneumatic Swellex pump. Steel straps are sometimes used to increase support capacity and cohesion. The immediate support effect, and simplicity of the operation, with minimum handling, are definite advantages to using Swellex instead of cable bolts. The method creates a small increase in normal cycle time, but the drilling and installation time are more than justified by the cost, risk and lost time associated with rehabilitating a caved roof. The collaboration of the production department was crucial to developing the method. Such experience shows that Swellex bolts can be efficiently used as a prereinforcement system in order to improve productivity and safety while excavating tunnels in incompetent rock. The method can be applied to systematically support roof, or to prevent caving from a nearby fault zone. The method is fast, improves safety, and can be easily integrated into development operations. Cooperation of the underground department for testing is paramount to the success of the technique, as the experience of the miners and supervisors is a valuable asset in improving excavation methods. ROCK & SOIL REINFORCEMENT

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Increased Output in Portugal The Neves Corvo Copper Mine in southern Portugal, owned by Somincor, has recently increased annual production from 2.1 to 2.3 million t. Reserves are around 30 million t of copper and 1.9 million t of copper and tin ore. Some 95% of the ore is being extracted using several mining methods: 60% of the tonnage comes from a modified drift-andfill method, 20% from benching, 10% from mini-benching, and the remaining 10% from mining of the sill pillars. Drift-and-fill mining is carried out by 13 face drilling rigs, of which nine are Atlas Copco Boomer units. Two Atlas Copco Boltec rigs for mechanized rockbolting, equipped with the latest Swellex hydraulic pumps, have been put into production, and the time taken to install a Swellex bolt in a pre-drilled hole at the mine is now less than 30 seconds. For benching and mini-benching, the mine is using three drill rigs, two of which are Atlas Copco Simba units. The two fully-mechanized Boltec rigs are installing 2.4 m-long Standard Swellex bolts in the roof and walls of the orebodies, with an average spacing of 1 m. Swellex bolts have been used at the mine for many years, and more than 60,000 are installed annually. They are popular because they offer instant support with easy and fast installation.

Systematic Support in Turkey At the Çeltek Coal Mine in Turkey, some 300 km north-east of the capital Ankara, the support system of a gate road has been changed from the traditional steel arches to systematic support with Atlas Copco Standard Swellex EXL bolts. This follows a joint effort involving Atlas Copco Turkey and a team led by rock support expert Professor Erdal Ünal of the Middle East Technical University. The aim was to introduce the high load-carrying capacity and yielding characteristics of Swellex to the country’s coal industry. A universal pull-tester developed by Professor Ünal’s team was used to show the superiority of the Swellex bolts in terms of speed, safety and economy. Time spent on roof support in a cycle decreased from two hours to between 20 and 30 min/m of advance in the gate road, resulting in an increased daily advance rate. ROCK & SOIL REINFORCEMENT

Project: Underground copper mine. Location: Southern Portugal. Mining method: Drift and fill with benching. Rock: Orebody roof and walls. Rock reinforcement required: Faster bolting to increase production. Rockbolt selected: Swellex. Rockbolting is the bottleneck in the production cycle, and several bolting units have to be used because of the long distances between the different faces, The mine blasts 25 faces/day to meet production targets, which means time is precious. Although the unit cost of Swellex bolts might seem expensive compared to some other rockbolts, they have proved to be the best solution in terms of the total installation costs.

At the Neves Corvo copper mine in Portugal, Sven Buskqvist, Wirsbo Stålrör AB, Antonio Rodrigues, Somincor, and Torres Marquez, Atlas Copco Portugal.

Project: Underground coal mine. Location: Çeltek, Asia Minor, Turkey. Mining method: Longwall mining. Rock: Seam roof. Rock reinforcement required: Replace steel arches with bolts. Rockbolt selected: Standard Swellex EXL. After experiencing the speed and ease of the Swellex bolt installation, the mine management and support crew agreed that the system also offers value for money. ■

At Çeltek mine in Turkey, a Swellex bolt is installed to demonstrate its unique ability to provide safe and immediate support.

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Removing Bottlenecks in Austria Crossroads of Europe With its position in the heart of Central Europe, Austria serves as a transportation hub for virtually any business needing to move goods across the continent. For traffic between the Balkan States and the north, or diagonally across Europe from east to south, Austria presents the shortest route. Indeed, the risk of traffic nuisance is such that trucks are currently banned from its highways during the night hours. In its efforts to upgrade to full European standards, Austria is building more dual carriageways, and driving parallel tunnels for a number of existing bi-directional tunnels across the country. In the tunnels, the latest in Atlas Copco technology is being employed, including the Rocket Boomer L2 C and self drilling anchors. Two such projects are the parallel tunnel recently completed at Graebern, on the Vienna to Klagenfurt section of the important A2 motorway which connects Vienna with Carinthia and Italy, and a twin tube tunnel project at Steinhaus, located near Semmering, a favourite skiing destination for the Viennese.

Project: Parallel tube for existing bi-directional road tunnel. Location: Graebern, on A2 Vienna-Klagenfurt highway. Excavation method: Drill/blast and mechanical excavation. Contractor: Joint venture of Ostu Stettin, Hinteregger, and Porr Tunnelbau. Rock: Mix of biotite gneiss and non-glaciated folded, faulted, and tectonised strata. Rock reinforcement requirement: Spiling followed by immediate face support. Rockbolts selected: Super Swellex and self drilling anchors.

Second Tube for Graebern The new 2.148 km-long tube was driven parallel to the existing Graebern tunnel in highly variable ground conditions. The faces at either end were in different strata, requiring a flexible approach to excavation and support. The contractors used some equipment, such as the Atlas Copco Rocket Boomer drillrigs, that was released following the completion of the 9.9 km-long Plabutsch tunnel, a similar dualling project on the A9 motorway at Graz. Around 1.5 km of the tunnel was excavated to standard 70 sq m section, 400 m of which was in excavation class 7 and needed a reinforced shotcrete or concrete invert, requiring an enlarged section of 78 sq m. ROCK & SOIL REINFORCEMENT

An oversize safety section in the centre of the alignment provides a third lane over a distance of 48 m, where vehicles may park in an emergency, or possibly turn around. They may also turn to enter a wide cross passage leading to the second tube, which is big enough for trucks.

Atlas Copco Rocket Boomer L2 C at Graebern south face.

South Attack At the south end of the alignment, where the rock was generally too soft for blasting, an Atlas Copco two-boom Rocket Boomer L2 C drilled for spiling and bolting in the top heading, so that the face could be mechanically excavated. The area was intensively folded and faulted, with a mixture of competent and 69

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Rock Support at Graebern Tunnel

incompetent rock. As there was no glacial cover during the past million years, glacial erosion did not remove the highly tectonised and incompetent parts present at the southern portal. The centre section of the top heading was generally left in place as a safety pillar, to support the tunnel face while sectional lattice arches were installed at 1.0-1.2 m centres, together with rockbolts and shotcrete. Part of the excavated face was also temporarily secured by 12 m-long self drilling anchors, which were grouted in place. For systematic bolting, self drilling or cement grouted anchors with lengths of 4 m or 6 m were used. When required, 25 mm-diameter, 4 mlong pipe spiles were set around the roof profile in 45 mm-diameter holes drilled by the Rocket Boomer L2 C. Any blastholes required were drilled using 45 mm Atlas Copco Secoroc bits. The top heading was followed by a 2.7 m-high bench and invert, which were excavated some 60-80 m back from the face, but periodically slipped back to 150 m behind the face.

Steinhaus at Semmering The Steinhaus tunnel is on the B306 Vienna to Bruck road, which passes through Semmering, a favourite skiing resort for the Viennese. The B306 is being upgraded, and will form part of the new S6 highway. This will connect with the San Miguel interchange on the section of the A9 Trans-European Highway between the main centres of Graz and Linz. The tunnel is twin-tube and 1.5 kmlong, on a double curving alignment that takes it into the side of the valley 70

North Face The north end of Graebern featured biotite gneiss, a more-competent metamorphic sedimentary rock with a high amount of quartz and feldspar. Predominantly, the rock mass was jointed and faulted, and so mostly decomposed and friable. Therefore, spiling with pipes was often an absolute necessity. In addition, Super Swellex 4 m-long bolts were set in the roof at the face as immediate support. Regular support comprised 15 cm of shotcrete with one layer of wire mesh and 4 m-long rockbolts. If spiling was required, lattice arches were erected, and shotcreted in place. A three-boom semiautomatic Rocket Boomer L3 C performed the support drilling duties at the north end, in addition to blasthole drilling. Drilling of a full round of approximately 130 x 2 m-deep holes in the top heading took an hour, in addition to a half-hour for charging and blasting. Blasting agents were dynamite and cartridged slurry, with 19 intervals of electronic detonators with millisecond delays at 80 milliseconds per step. The drilling rounds were set up using an array of seven lasers to establish a perfect profile. in which the village of Steinhaus is located. It has been constructed by Bilfinger Berger for the Austrian highways authority. The rock quality is variable, generally soft and non-glaciated, comprising chalk, phyllite, calcite and quartzite, with a maximum cover of 60 m. The tunnels accommodate a two-lane highway in each direction. There are three cross-passages, with the middle one having a large cross-section to facilitate the switching of trucks between tubes in emergency situations. ROCK & SOIL REINFORCEMENT

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The full 80 sq m section of each main drive was achieved with top heading, bench and invert excavations. The faces passed beneath some village houses with around 50 m cover, and two blast vibration monitoring stations were set up.

Cautious Advance Work at Steinhaus commenced at the west portal with a 47 m-long central pilot tunnel, within which the pillar between the two main tubes was cast using self-compacting concrete. The separation over the first 50 m of alignment was 2 to 4 m, increasing progressively to 60 m at the halfway mark. The rock pillar on the second 50 m of drive was anchored using pre-stressed bolts, tightened by plates on both sides. The drillrig fleet comprised three lateseries Atlas Copco Rocket Boomer 352S, and one newer Rocket Boomer L2 C. They spent 80% of their time drilling for rock reinforcement because, generally speaking, only 10-20 blast holes were required in the faces of the top headings. The faces, which were mechanically excavated, were secured by up to nine 16 ft-long self drilling anchors with mortar injection. Roof and side support was achieved mainly with grouted rebars and self drilling rockbolts from Atlas Copco MAI, and five MAI M400 water mixing pumps were used for grouting. In order to maintain reasonable underfoot conditions, a temporary shotcrete invert reinforced with steel mesh was laid in the top headings, every 4 or 5 arches on advance. Drainage holes were drilled in the face whenever necessary. Usually, three or four arches were set at 1.5 m intervals in each face during a 24 h cycle of three shifts.

Umbrella Working At the 90 m mark on the south drive, a 20 m-high Karst cavity was encountered, which, fortunately for the tunnellers, proved to be dry. The drillrig was pulled back to drill over the face and into the cavity. Some 30 cu m of 8 mm concrete was then pumped through the drillholes, using one of the shotcrete jumbos. Advance over a 10 m stretch beneath the filled cavity was protected by arches of 20-30 spiles made of 51 mm x 8 m-long R32 pipe installed at 2 m increments. ROCK & SOIL REINFORCEMENT

Project: Twin tube 1.5 km-long road tunnel. Location: Steinhaus on the B306 Vienna-Bruck road through Semmering. Excavation method: Mechanical excavation with some drill/blast. Contractor: Bilfinger Berger. Rock: Soft, non-glaciated chalk, phyllite, calcite and quartzite. Rock reinforcement requirement: Forward support and immediate face support. Rockbolts selected: Self drilling Atlas Copco MAI rockbolts.

Once into more competent ground, the drillrigs were able to deliver 80-90 holes/round in the top headings, drilled to depths of 1.5-1.7 m. Blasting was by millisecond and long delay non-electric detonators and encapsulated slurry main charge. The bench followewd at between 90 m and 220 m behind the face, where the temporary invert was ripped out by an excavator with hydraulic hammer. A concrete pump was stationed at each bench as a convenient way of pumping shotcrete past the ramp position, from where a mixer truck transported it to the face jumbo. Self drilling rockbolts have become very popular in recent years, and are now used in a number of different applications, for both surface and underground drilling. In tunnels, their primary use is for advance support of extremely friable rock, or in formations where the drill hole will collapse before a normal rockbolt can be put in place. The bolt is made up of five essential parts: a threaded bolt, a single-usage drill bit, a connection casing, a screw plate and a nut. The rockbolts are available in standard lengths, by the metre from 2-6 mlong, with special customer-designed lengths of up to 12 m. ■

Rocket Boomer 352S at Steinhaus portal.

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Swellex in Extreme Temperatures Hot and Cold Mining Swellex rockbolts are used successfully in hot and cold extremes on both sides of the world. Not only has the bolt been found to perform to full capacity in all temperature conditions, but it has also found favour with the operators. Because of its light weight, and speed of installation, the operators are finding that Swellex does not overexhaust them under the rigorous conditions in which they work. Another bonus is that grout mixes and resin ampoules are not required, significantly reducing the transportation costs to remote mines, and limiting the fetching and carrying to be done under extreme conditions. This is truly a market sector where Swellex is unbeatable!

Project: Raglan Katinniq nickel mine. Location: Northern Quebec, Canada. Mining methods: Longhole stoping, cut and fill. Operator: Falconbridge Nickel. Rock: Blocky with permanently frozen fissures. Rock reinforcement required: Long bolts not requiring resin. Rockbolt selected: Swellex Mn24 and Connectable.

Performing in Permafrost The Raglan mine is located on the remote Ungava Peninsula of northern Quebec, where the mean annual temperature is minus 10°C, with an ambient temperature underground of minus 15°C. It is a conventional shovel-and-truck open pit, with an underground mine at Katinniq, where there are two mining methods in use: long-hole stoping and cut and fill. Although large stopes are not typical at the mine, a stope opened in 2003 measured 160 m-long x 63 m-wide. The orebody is wide, with limited height and strike length, and the footwall dips at a 45° angle, making most of it unfavourable for development of longhole stopes. At any given time, Katinniq has 10-15 stopes in operation, with only one or two being the more productive longhole stopes. The rest are cut-and-fill which, despite being more labour intensive, account for over half of the 50,00055,000 t/month of ore produced. Katinniq has reserves of 19.5 million t, grading 2.85% nickel and 0.79% copper, as well as significant recoverable cobalt and platinum-group metals. The mine is accessible by air, and linked by an allweather road to ship-loading facilities at ROCK & SOIL REINFORCEMENT

Location of Raglan Mine in Northern Quebec.

Deception Bay, about 100 km to the east. The nearest supply town is RouynNoranda, about 1,600 km south. With the ground permanently frozen to a depth of 425 m, rockbolting at Raglan could be a difficult and time-consuming procedure, without Swellex. Although the cold makes working conditions difficult, the ground is more stable because there is no water moving through fissures in the rock. The normal maximum stope size is 30 m-wide and 105 m-long, so ground stability is important. The host rock is extremely competent, with no ground stress problems. With joint spacing over 2 m, the main rock support consideration is the risk of falling blocks. The mine generally uses 2.4 m bolts for stability, but these may increase to 4 m-long or 5 m-long bolts when big blocks occur. Previously, the mine used mechanical bolts and rebar set in resin for rock support. However, the mechanical bolts required periodic re-tensioning to be effective. This was labour intensive, and the use of resin posed significant logistical and transportation problems. 73

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Easy Installation After an extensive research and testing period, Raglan made the switch to Swellex bolts in 1999. Since then, they have been using Swellex almost exclusively, in order to ensure consistent quality of rockbolting while maximizing productivity. At Raglan, all drifts are screened and all stopes are bolted. The mine is budgeted to use: 6,500 of the 600 mm Swellex bolts for

Project: Toyoha lead/zinc mine. Location: Hokkaido, Japan. Mining method: Sublevel stoping. Rock: Volcanic host. Rock reinforcement required: Easily installed non-grouted rockbolts. Rockbolt selected: Standard and Midi Swellex.

Hot Work in Hokkaido Drillers at the Toyoha mine in Japan get more than a warm welcome when they arrive for work each day. Due to the volcanic rock in the area, the mine generates rock temperatures of 130°C, and a heatwave follows the opening of any new areas. Humidity is extremely high, and it is not unusual to see jets of steam coming from newly drilled rockbolt holes. These are, indeed, extreme conditions under which to install effective rock reinforcement! Toyoha, which is the world’s largest producer of the rare metal Indium from its lead and zinc operations, carries out sublevel stoping in the steeply inclined orebody, where drifts are 3 m-high and 4 m-wide. In these difficult conditions, and since neither cement grout nor resins can be easily handled in such high temperatures, the mine uses Swellex rockbolts from Atlas Copco for rock reinforcement. Drilling and installation of 1.5 m-long Swellex bolts in the normal pattern used at the Toyoha mine to stabilize a round is performed by a single miner in just 32 minutes. This is a very fast production rate, especially considering the high temperature and humidity. The key is in the Swellex system itself, which enables bolt after bolt to be expanded in just 22 seconds apiece. The mine management insists that only Swellex can give superior safety in hot 74

fastening screens in the 5 m-wide drifts; 50,000 of the 1.6 m bolts used largely in wall rock; 62,000 of the 2.5 m bolts used for the back; and 2,000 of the 3.8 m Super Swellex bolts as needed. Raglan uses brine to expand the Swellex bolts in order to avoid freezing problems. This has not resulted in detectable corrosion in the bolts, and recent pull tests confirm this. Swellex Mn24 has now replaced Super Swellex at the mine.

rock such as this, and rates the easy and trouble-free installation system as a big plus. Toyoha uses up to 2,000 bolts/month of the 2 m-long Midi Swellex type, which are well suited to the large diameter explosives now being used. The number of holes required at the face has been reduced as a result. The operators prefer Swellex bolts because they can be set in the hot conditions without using a work platform, or heavy tools and equipment. Two-thirds of the bolts currently used in the mine are Swellex. They are lightweight, easy, quick and safe to work with, and do not require grouting, keeping the work area clean. ■

Installing Swellex at Toyoha Mine, Hokkaido, Japan.

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Coated Swellex Examined Unique Testing Opportunity Not far from Orebro in central Sweden lies Kvarntorp mine, a disused underground sandstone mine that has been converted as an archive store. The rock is sedimentary, occurring in horizontal layers, with sandstone overlain by shale. The sandstone is porous, but relatively homogeneous, varying from white to light grey in colour. It is lightly laminated with thin clay seams, which are often not more than 1 mm-thick. The groundwater is corrosive, so, when Coated Swellex rockbolts became available, the mine was quick to realize the advantages, and began using them in 1987. Recently, tests were conducted on two of these bolts that had been installed nine years earlier, and it was found that virtually no corrosion had taken place.

making it difficult to establish the exact conditions to which the bolts have been exposed.

Support Investigation

Rock Reinforcement

A few years ago, owner Yxhult AB experienced a number of small falls of roof at Kvarntorp mine. It was found that several point anchor expander bolts installed in 1968 had rusted through 0.8 m inside the rock, and had fallen out. The Swedish industrial safety authority requested Yxhult AB to launch an investigation to determine the extent of the problem, and to recommend a rock support programme that would ensure the safety of people working underground. The company contacted SvBeFo, the Swedish scientific organization involved in studying the behaviour of rock in mining, construction and building, to solicit their involvement. The Stockholm-based consulting company Sycon was contracted to carry out the investigation, and Atlas Copco agreed to take part in the project. The ground water in Kvarntorp seeps through the overlaying shales, which have relatively high sulphur content, and is known to be corrosive. There was a considerable amount of water present in the rock during the excavation of the openings, but this had disappeared over the years,

Support was exclusively by rockbolts, installed vertically as the drives and rooms were excavated. Expander type point anchor bolts were used initially, then the mine switched to cement-grouted rebar. These were used from 1967 to 1969, when they switched to resin-grouted rebar, and in 1987 to Atlas Copco Swellex bolts. The following rock bolts and grouting agents were used during the production phase of the mine: cement grouted rebar, 2.2 m-long; resin-grouted rebar, 2.2 mlong, with two Celtite cartridges; resingrouted rebar, 1.8 m-long, with two Celtite cartridges; and Coated Standard Swellex, 1.8 m-long. During this development of rock support, point anchor expander bolts proved entirely inadequate, and were replaced by cement-grouted rebar. The disadvantage of cement-grouted rebar is that it is messy, time-consuming, and does not provide any support before the cement hardens. In 1969, the mine switched to resin cartridges as the grout medium used to install rebar dowels. This has the advantage of providing more immediate support.

ROCK & SOIL REINFORCEMENT

Cross-section of bolt No 1 shows corrosion described as insignificant.

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their minimum specified breaking strength during these tests.

Overcored Bolts

Internal surface of bolt No 2 shows it is practically free from corrosion.

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However, it is still arduous and, as with cement, there are high wastage factors. Both resin and cement grouting of rebar present the operator with a number of installation quality concerns. These range from inadequate grout in the hole or, as in the case of resin, “over-spin” or “underspin”, both of which adversely affect the support capability of the installation.

It was then decided to over-core two Swellex bolts to establish their condition. These were forwarded to the Swedish Corrosion Institute for further examination. All Swellex rock bolts are stamped with an alpha-numerical identification. The recovered bolts were marked 1.8 930125 B STD Sweden, showing that this was a 1.8 m-long bolt manufactured in Sweden on January 25, 1993. They were recovered in mid-May, 2002, so were in the rock for a little over 9 years. At the Corrosion Institute, the rock cores were removed and the bolts visually inspected, after which cross-sectional pieces were sawn out for more detailed inspection. Observations by the investigating engineer were that uniform corrosion on the outside of the bolts was very small, less than 0.1 mm-deep. Internal corrosion was mostly non-existent, with a few small shallow patches. One of the bolts had two small local corrosion penetrations that did not affect the breaking strength.

Coated Swellex

Conclusion

Swellex rockbolts are manufactured from folded steel tubing that can be inserted in the drill hole manually or mechanically, and expanded with high-pressure water. The installation takes a few seconds, and the expanded bolt is pressed tightly against the rock, deforming to the irregular sides of the drill hole. This provides guaranteed full column support, as the water pressure is applied equally throughout the bolt. Coated Swellex has a rubberized bitumen coating on the outside of the bolt. As the bolt is expanded, this coating, which is semi-viscous, is pressed into the microstructure of the rock on the inside of the drillhole. The coating provides a barrier between the rock and the bolt that prevents the ingress of corrosive water. As the coating completely covers the outside of the bolt, and the bolt expands over its full length, the result is a guaranteed quality installation. It was decided to perform pull tests on a number of bolts at Kvarntorp mine to test their integrity after having been in the rock for nine years. The Swellex exceeded

The conclusion was that, after more than nine years in the corrosive environment of Kvarntorp mine, Coated Swellex bolts had not lost any of their strength or support capability. They were not involved in any of the rock falls that had occurred. Sycon made the following recommendation: the area where the rock falls had occurred should be re-bolted using 1.8 m Coated Swellex bolts fitted with 150 mm x 150 mm bearing plates, installed 5 bolts/row, with 2 m between each row. The result of this investigation establishes Coated Swellex rock bolts as long term support suitable for use in a variety of environments. Situations differ from mine to mine, and from tunnel to tunnel, and require careful study by qualified people. However, there is no doubt that mines and tunnels with aggressive environments can benefit from the many advantages of Swellex rockbolts. The full report from the Swedish Corrosion Institute is available from Atlas Copco in English upon request. Contact Turgay Ozan [email protected] and ask for report number 80 103 (rev 1). ■ ROCK & SOIL REINFORCEMENT

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NEVADA, USA

Tunnelling with Nuclear Quality Assurance Stability for a Hundred Years The construction of the Exploratory Studies Facility (ESF) at Yucca Mountain has set new quality standards for tunnelling operations. It has been proved possible to build a tunnel according to nuclear quality standards, while at the same time maintaining flexibility for scientific investigations and acceptable tunnelling productivity. The 7.8 km-long ESF tunnel has been driven by TBM within the rock formation that is being evaluated to determine suitability for the final repository, and may become a part of the repository itself. The requirements on long-term stability for radiological safety of a future repository, in this case equal to 100 years, resulted in rejection of most available ground support products. Instead, Super Swellex rockbolts were chosen, together with welded mesh and a rolled steel channel, for permanent support in the ESF tunnel. A similar system was used to support the more recent 2.681 km-long East-West Cross Drift tunnel to investigate ground conditions over the proposed repository. Tunnelling at Yucca Mountain will probably go on for many more years, adding invaluable practical experience to the world’s pool of knowledge of how to construct repositories for nuclear waste. With nuclear waste accumulating in many other countries, this project is being watched very closely by a number of agencies around the world.

Underground Laboratory Yucca Mountain, located in the Nevada desert approximately 160 km from Las Vegas, is today the only site that the US Department of Energy (DoE) is studying for the nation’s first permanent high-level nuclear waste repository. The Exploratory Studies Facility (ESF), part of the Yucca Mountain project, will be ROCK & SOIL REINFORCEMENT

Project: Nuclear waste repository investigation. Location: Yucca Mountain, Nevada. Excavation method: TBM and roadheader. Contractor: Kiewit/Parsons Brinckerhoff. Rock: Volcanic tuff. Rock reinforcement required: Systematic roof support with 100 year stability. Rockbolt selected: Super Swellex.

an underground laboratory for engineers and scientists to help determine the ability of natural and engineered barriers to safely store spent nuclear fuel and high-level radioactive waste in a geologic repository. A large percentage of the ESF tunnel design has been done according to a Nuclear Quality Assurance program (‘Q’-standard), similar to that used for nuclear power plants. Ground support is ‘Q’ classified. This has impact on ground support design, type of ground support chosen, procurement of ground support products (including lifetime documentation and traceability of materials used in manufacturing), installation of ground support, and

Curved drive at Yucca Mountain ESF tunnel, close to Las Vegas.

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The data gathered, together with results and conclusions from the investigations, will assist in the final decision on whether Yucca Mountain is suitable for a nuclear waste repository. Yucca Mountain consists of layers of volcanic tuff, with a total thickness of at least 1.8 km. Most of the excavation will be in the uppermost and middle Topopah Spring formations, located approximately 300 m below the surface. This is the potential subsurface repository horizon, and is more than 100 m above the groundwater table. The ESF has been geologically mapped along its total length, using a 55 m-long gantry built into the TBM trailing gear.

ESF Tunnelling Progress

Part of the ESF main tunnel with typical ground support installed.

verification of the function of the products used. A 7.8 km-long tunnel, which is a part of the ESF, has been completed. Investigations to determine the suitability of Yucca Mountain as a potential repository are well underway, following which a repository licence application will be submitted to the Nuclear Regulatory Commission.

Exploratory Studies Facility The 7.8 km-long, 7.6 m-diameter ESF tunnel was excavated by Kiewit/PB using a CTS TBM to a design by TRW Environmental Safety Systems Inc. By examining the surface and the underground space that will be accessed via the ESF, the scientists will be able to thoroughly investigate rock strength and movement, groundwater, and earthquake and volcanic activity. Other factors that will be considered in the site characterization include: geologic history; geologic information; public safety and concerns; local economic and socio-economic impacts; environmental concern; ease and cost of constructing and operating the site; and the effect of high temperatures on the strata. 78

The TBM was launched from a 60 m-long drill/blast starter tunnel. The first part of the ESF tunnel, the North Ramp, was driven at a 2% downgrade against rock beds dipping 2° to 15° to the east. The first 200 m of tunnelling were difficult, and steel sets were installed on 1.22 m centres. The Bow Ridge Fault, encountered approximately 200 m into the mountain, was filled with a soil-like, weak tuffaceous material, having an unconfined compressive strength as low as 1.4 MPa. Even though the fault had slipped approximately 100 m, it was only a few metres wide. After crossing the fault, the TBM entered softer material in which steering was difficult. Ground was lost above the TBM, necessitating backfilling and grouting of the void created. For about 1,000 m, tunnelling was through the Imbricate Fault Zone, which proved very difficult. Minor faulting events had caused through-going joints, oriented in the same direction, closely spaced and nearly parallel. This, in combination with low stressed rock, led to block fallouts, and steel sets combined with steel lagging had to be used extensively. Close to the Ghost Dance Fault, two testing alcoves were excavated to gain access to the fault deep inside Yucca Mountain. After approximately 2,700 m of tunnelling from the entrance at the North Portal, the TBM reached the Topopah Spring potential repository host rock at approximately 300 m depth. In this formation, 3,000 m of the ESF main tunnel was ROCK & SOIL REINFORCEMENT

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constructed using Swellex bolts, wire mesh and rolled steel channels for support, and high advance rates were achieved.

NQA System Applied to Ground Support Since the ESF is an underground laboratory, where rock characteristics are studied, the DoE stresses that ground support must not interfere with the geotechnical and geological testing. Also, the final ground support system must be installed as the tunnel progresses. The tunnel must be reinforced in such a way that stored nuclear waste could be retrieved 100 years after it is put in place. Hence, the ground support must ensure long-term stability and maintainability. Cement grouted rebar bolts cannot be used in areas where scientific investigations will take place, because the grout may penetrate rock fractures and contaminate test results. Also, due to the curing time of the grout, this type of bolt cannot be tested immediately after installation. There is also a ban on the use of epoxy resin based rockbolting systems, since the amount of organic material in the tunnel has to be minimized in order not to pose any threat to nuclear waste packages. The use of shotcrete is limited, since it can interfere with geological mapping and geochemical tests. For many such reasons, Swellex rockbolts, manufactured by Atlas Copco, were approved for permanent rock reinforcement in the ESF tunnel. Procurement of ground support materials requires lifetime documentation and traceability, from materials used in the manufacturing, to fully inspected installations. Records are kept in a thorough and precise way, and internal and external audits are carried out to certify that everything is done according to specifications and procedures.

tion to this, steel reinforced concrete inverts were installed as the TBM advanced, providing the surface and track to support the TBM trailing gear. About 70% of the tunnel has been supported by Super Swellex rockbolts, with steel sets used for the remaining 30%. More than 20,000 Super Swellex bolts have been installed in the ESF tunnel. The Super Swellex rockbolt is a friction bolt manufactured by Atlas Copco. The bolt is made from a welded circular steel tube, then folded on itself into a ‘W’-shape to decrease the diameter. Bushings are then pressed onto the collapsed steel tube, and the ends sealed by welding, to create a

Each steel set and position for the Super Swellex bolts has a number, for the installation report.

Installing Atlas Copco Super Swellex from the TBM bolting station in competent ground.

Ground Support System As main support, 3 m-long Super Swellex bolts complete with the domed Super Swellex face plate on a 1.5 to 1 m pattern, depending on ground conditions, were used, together with a 250 mm rolled steel channel and welded wire fabric (WWF). The steel channel and WWF prevent rocks falling from the roof of the tunnel. In addiROCK & SOIL REINFORCEMENT

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spacing was 1,500 mm, with allowable maximum of 1,687 mm. Spacing and pressurization of the bolts was monitored to verify that they were properly installed, with a pressure between 290 and 310 bar. The Swellex pump unit was checked with a calibrated gauge at least once a day by the Shift Engineer to ensure that the pump was giving the correct pressure. During tunnelling, five out of every 100 rockbolts installed were tested to check if the proof load was reached. If the TBM entered a new geological formation, five destructive pull-tests were carried out to verify that the Swellex bolts met the minimum anchoring requirement. Complementary to this, 20 non-destructive pull-test were made. Not a single bolt failed in the pull-out tests.

Future Tunnelling

Using the drill feed to press the screen against the rock while installing a Swellex rockbolt.

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confined space inside the bolt. A hole is then drilled in the lower bushing. When the bolt has been positioned in the borehole, water is injected through the hole drilled in the bushing, causing the tube to unfold. At 30 Mpa the bolt is full expanded in the hole, and the pump automatically stops. As the pressure inside the bolt reaches 30 Mpa, the steel tubing adapts to the shape of the borehole, and may consolidate the surrounding material while it expands to fit the irregularities of the hole. The resulting frictional and mechanical interlocking reinforces and increases the stability of the rock surrounding the drilled hole. When each batch of bolts arrived at site, the Kiewit/PB Quality Control group carried out thorough tests and inspections to verify that they had not been contaminated or damaged, and that the dimensions were according to the specifications. Rockbolt drilling and installation was carried out at two stations on the TBM. At the first station, four Swellex bolts were installed, together with the screen and the channel. At the second station three holes were drilled, and the remaining three bolts installed, including the bolt located at the highest point in the tunnel. The nominal

Further tunnelling since completion of the ESF tunnel has included the 2.681 km-long exploratory East-West Cross Drift Tunnel across the potential repository. This employed a 5 m-diameter Robbins hardrock TBM, which started at an intersection with the North Ramp of the ESF and, after an initial curve, followed a tangential alignment, and crossed over the proposed repository block west of the main loop of the ESF tunnel, to terminate in the Topopah Springs geological formation. Once again, Super Swellex 1.8 m-long rockbolts were used for ground support on a 1.2 m x 1.2 m grid over the full crown, with welded wire mesh and 1.2 m-long steel channels. A total of 20 steel sets was required in only one area of the tunnel, where the Super Swellex bolts could not provide long-term support. The TBM average advance was 25 m/day over 106 mining days, with a best shift of 34.6 m, best day of 73.2 m, and best week of 266.7 m. The TBM was mining for only 25% of the time, due to the concurrent scientific and environmental experiments being carried out. The design of the repository is not yet finalized. However, a system of tunnels totalling more than 200 km is being discussed in which more than 1 million bolts will be installed over a period of 20 years. Following the signing of the Yucca Mountain Resolution on 23rd July, 2002, the Nuclear Regulatory Commission is considering licensing the repository. ■ ROCK & SOIL REINFORCEMENT

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Swellex Versatility in Tunnelling Fast Installation and Immediate Support Since the introduction of the Atlas Copco COP series of high-performance rock drills, drilling is no longer necessarily the bottleneck in tunnelling operations. Mounted on sophisticated rigs, drilling preset hole patterns with contour and profile control, these machines have encouraged their owners to reappraise every aspect of the face operation. Inevitably, focus has been brought to bear on the rock reinforcement systems in use, and their impact on overall productivity. Fast drilling and slow rockbolting rarely make economic sense, not least because expensive equipment may be underutilized, while conditions are made safe. In this environment, Swellex bolts come into their own, as the most cost-effective solution. They are fast to install, and give immediate support, making the face available for further operations in the shortest possible time. The following case studies trace this theme, through difficult motorway tunnels in Germany and Spain, fast-advancing railway tunnels in China and Switzerland, and in the new road system on the volcanic Atlantic island of Madeira.

Project: 1.1 km and 2.3 km twin tube, three-lane road tunnels, 150 sq m section. Location: Motorway between Germany and Czech Republic. Excavation method: Drill/blast, top heading and benching. Contractor: Walter Bau. Rock: Syenite, fractured and weathered in places. Rock reinforcement requirement: Immediate support, due to large span. Rockbolt selected: Super Swellex, and Boodex close to the portals.

Driving from Dresden to Prague The new 200 km-long A17 autobahn under construction from Prague in the Czech Republic to Dresden in eastern Germany will provide the Czech capital with rapid access to northern Europe and the North Sea ports, and will also form a vital section of the Trans-European road network. The most difficult part of this section is the 8.85 km-long alignment from Gorbitz to Sudvorstadt, where contractor Walter Bau undertook the twin-tube, three-lane 1.1 km-long Doelzschen and the 2.3 kmlong Coschutz tunnels using sequential excavation techniques. Both tunnel alignments are predominantly in syenite, a hard rock with around 10% quartz content. They were each ROCK & SOIL REINFORCEMENT

Atlas Copco Rocket Boomer 352 umbrella drilling at Dresden.

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driven by drill/blast in a single direction from twin portals. Top headings of 72 sq m section preceded the benches, advancing mainly in soft, mixed ground requiring a lot of support. The full, flattened ovoid section of 150 sq m was achieved with a 41 sq m following bench, and a 37 sq m invert. A total of eight Atlas Copco Boomer 352 drillrigs were used for face drilling, rockbolting, and umbrella drilling. Face drilling in the top headings was undertaken by two Atlas Copco 352 Boomers, standing side by side. The added flexibility of the two-rig system speeded up the drilling and charging process, to the extent that the entire excavation cycle could be completed in 2.5 h. This facilitated up to four rounds in each 24 h period, leaving 14 h available for support work and rock reinforcement, much of which was scheduled for the night shift. Heavy-gauge steel arches were set in the top headings, with two layers of Q378 steel mesh and two applications of shotcrete to roof, sides and floor. A row of 4 m-long Swellex rockbolts was set in a 22 m-long radial arch at the face to give

Project: A dozen km-long road tunnels, each around 60 sq m section. Location: Madeira Island, a self-governing region of Portugal. Excavation method: Drill/blast, mostly at full section. Contractors: Zagope, Tamega, Epos, and Avelino Farinha & Agrela. Rock: Volcanic formations with lava streams, fractured basalt, ashes and tuff. Rock reinforcement requirement: Versatile system to cope with extremely irregular geology. Rockbolt selected: Standard Swellex.

Fast Bolt for Madeira The chain of mountain peaks that forms the Madeira Islands, an autonomous Portuguese region with its own government, rises some 5,300 m from the bed of the Atlantic Ocean. Madeira is the largest island of the archipelago, and is 57 kmlong and 22 km-wide. It has a population of around 260,000, of whom 120,000 live in the capital, Funchal. The islands are located 545 km from the coast of north Africa, having been formed by volcanic eruption. The resulting mountains are steep, and plunge from elevations of 82

early support, and 5% of these were randomly tested at 10 t pulling pressure, as a routine stipulated in the contract. Where immediate support is required, Swellex rockbolts can be in place and providing full support up to seven hours earlier than conventional cement grouted bolts. This was invaluable in the softer ground towards the ends of the tunnels, where pattern rockbolting was used. Elsewhere, in better rock conditions, the contractor favoured the system because Swellex bolts are fast to install and offer guaranteed support. The consistent use of top specification rockbolts was reckoned to improve the overall quality and integrity of the tunnel. When the ground got too soft for conventional excavation, two Atlas Copco Boomer 352 machines equipped with drillrod cassettes were available. These drilled 15 m-long holes around the periphery of the crown, using Odex eccentric bits and extension drillrods. The holes were then lined with perforated steel tubes, through which cement grout was pumped to form a protective umbrella. Beneath this umbrella, a 12 m advance could safely be made.

1,800 m into deep valleys. Roads are tortuous and often dangerous, and travelling is fraught with problems. Inland routes are slow and winding, and the coastal roads are fringed by high cliffs, and are prone to rock falls caused by winter floods from the mountains. Tunnels have been employed to carry the roads beneath the mountains and under the cliffs, levelling the routes and making them safer. The picturesque Via Rapida road from the airport to the capital Funchal is a typical example, running over bridges and through 22 tunnels, with a further six to be constructed. The new Via Rapida tunnels were built by three contractors: Zagope; Tamega; and Avelino Farinha & Agrela. Rocket Boomer 104 and 135 drillrigs were used, two of a total of eleven Rocket Boomer rigs that are employed on tunnelling projects in Madeira. Atlas Copco Swellex rockbolts are also a favourite reinforcement method in the typical strata of volcanic basalt and tuff. The Porto Moniz project, near São Vicente, comprised five tunnels up to 1,269 m-long. It was designed to divert ROCK & SOIL REINFORCEMENT

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heavy traffic from the scenic coastal road that runs under the cliffs by the ocean. This is a dangerous route, not least because of rock falls and floods. Portuguese contractor Tecnorocha used three of their fleet of nine Atlas Copco Boomer drill rigs equipped with COP 1238 rock drills to develop the tunnels. Blastholes were 4.2 m-deep, and advance varied between 3.5 m and 4 m/blast, resulting in an average advance of 7 m/24 h. Standard Swellex rockbolts, together with mesh and shotcrete, provided the permanent support, because they proved to be the most cost-effective solution. The speed of installation enabled Tecnorocha to finish the project sooner, and utilize their equipment more efficiently. The Ecumeada Tunnel, built through the Serra de Agua mountain in the centre of the island, is the longest single tunnel at 3.1 km, and has cut driving time from the north to the south coast by 20 minutes, making the journey much safer. Contractor EPOS excavated the tunnel by drill and blast, using Standard Swellex rockbolts, together with steel fibre reinforced shotcrete when the rock was good enough, and steel arches, together with wire mesh and shotcrete, when it was not. The volcanic rock formations are prone to change very quickly, and heavy water inflows were often experienced. The geotechnical engineer reported that the Swellex bolts proved very quick and easy to install, and provided good reinforcement in the constantly changing rock conditions. Ponta do Sol was a project comprising three road tunnels, with a total length of 1,900 m, where Avelino Farinha & Agrela used an Atlas Copco Boomer 352 for drilling the blast holes and bolt holes. Rock reinforcement comprised Swellex rockbolts, wire mesh and shotcrete. A

Hong Kong Cannot Wait Major new tunnelling operations in Hong Kong have used Atlas Copco drilling and bolting equipment fitted with the very latest computerized capabilities, together with Swellex rockbolts and full service back-up agreements. The 5.5 km, 110 sq m Tai Lam tunnel on the West Rail development was a Nishimatsu-Dragages joint venture, with the two contractors driving the single ROCK & SOIL REINFORCEMENT

Boomer 352 installed 15 bolts/h with a pneumatic Swellex pump, and up to 30 bolts/h using a hydraulic pump. Very large water inflows were experienced, and a waterproof plastic membrane was installed prior to the final 25 cm-thick, cast-in-place concrete lining. The heads of all bolts were cut away to provide an even surface for the membrane.

Porto Moniz, Madeira, where topography favours tunnels as a means of shortening distances.

Projects: Tai Lam tunnel–West Rail, 5.5 km, 110 sq m. Black Hill and Pak Shing Kok tunnels, 20.5 km on the MTRC (metro), 80 sq m. Location: Hong Kong, China. Excavation method: Drill/blast, full section. Contractors: Nishimatsu-Dragages joint venture, Dumez. Rock: Mainly hard rock, such as granite. Rock reinforcement requirement: High productivity systems to speed up excavation. Rockbolt selected: Standard Swellex.

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Rocket Boomers WL3 C drilling rockbolt holes at Tai Lam in Hong Kong.

tunnel from opposite ends. Nishimatsu’s stretch was 2.6 km-long, and they achieved an average advance of 200 m/month with Rocket Boomer WL3 C rigs. Their best monthly performance was 230 m, with two blasts/day, using the fully-automated ABC mode for 80% of the time. Atlas Copco agreed a drillmetre contract linked to spare parts and rock drilling tools supply, as well as an around-theclock service arrangement. The Black Hill and Pak Shing Kok tunnel projects on the MTRC Tseung Kwan O Extension are part of a 12.5 km-

Holding Fast on Slipping Ground In Spain, the Autovia del Cantabríco motorway will eventually run some 500 km along the coast of the Bay of Project: 1.3 km El Fabar, twin tube road tunnel. Location: Northern Spain Excavation method: Drill/blast, top heading and bench. Contractor: Joint venture Dragados and FCC. Rock: Weak strata of slates and fractured limestone. Rock reinforcement requirement: Anchorage capacity, even in clay-bearing formations. Rockbolt selected: Standard Swellex.

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long, five-station extension which will serve a population of 340,000. A major factor in the progress of both projects was the performance of six Atlas Copco L2 C Rocket Boomer rigs. The Black Hill tunnels total 8 km, with four tunnels designed to serve the up and down trains of two MTR lines, and a centre siding. Here, six junction chambers, and two crossovers with 80 sq m cross sections, were excavated by joint venture contractors Dumez of France and Chun Wo of Hong Kong. The contractor used three new Rocket Boomer L2 C rigs for face drilling, and two second-hand Boomer 281 units for rockbolting. The rigs drilled 4.6 m rounds, and some 30 m/day were achieved for all four tunnels, with a best daily advance for a single face of more than 12 m. The Pak Shing Kok tunnels project was also a complex job, with nine tunnels totalling 6.4 km built by a jv of Hyundai and Kier International. Tunnelling was carried out in a mixture of volcanic tuff and granite, using three Rocket Boomer L2 C drillrigs with two booms, drilling to a depth of 4.2 m. Poor rock areas required around 60,000 cu m of fibre-reinforced shotcrete, and some 5,000 Atlas Copco Swellex rockbolts. Swellex was chosen primarily for its fast installation time of around one minute, compared to the 10-15 minutes for conventional bolts. Although the tunnels are amongst the most complicated on the MTR, the contractor was able to maintain an average progress of 550 m/month, completing the job in less than a year, compared to the forecast of 18 months.

Biscay, from San Sebastian in the east to La Coruña in the west, linking the cities of Bilbao, Santander, Oviedo, Gijón and La Coruña. The project and works promoter is the Ministry of Public Works. Parts of the eastern section are already open to traffic. Other sections, like the 65 km-long stretch from Ribadesella to Gijón, are under construction. The 1.3 km-long El Fabar twin tubes, in predominantly fractured limestone with slate and quartzite, were driven by a jv of FCC and Dragados using Atlas Copco Rocket Boomer L2 C drillrigs on each face. Three Atlas Copco Wagner ST 8A Scooptrams were employed shifting the muck. ROCK & SOIL REINFORCEMENT

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The 54 sq m top headings were driven some 700 m from the east end, then the whole operation moved to the west portals. The top headings were holed through in the middle of the tunnel before bench excavation started. The Scooptrams were fully effective at this range and section, enabling the normal number of load/haul operators to be halved. The Boomer L2 C units drilled 40-50 blastholes per round, with the fractured rock limiting depth to 1.5 m, and steel arch support with mesh and reinforced concrete was required. For every metre of advance, ten 3.6 m Swellex rockbolts were installed for instant support, in holes drilled by the Boomer rigs. A 24 h/day, 6 day/week schedule was operated at the site, with the average daily advance 4 m on each face.

AlpTransit, Largest European Tunnelling Project Lotschberg was being driven from the south by a 9.38 m-diameter TBM from the Raron portal and a similar machine from the Steg lateral adit. Both of these were gripper TBMs, each equipped with work platforms with anchor drills immediately behind the face. Rockbolting and meshing was undertaken 4.2 m behind the cutterhead, and this is followed by independently operated shotcrete robots, which sprayed a concrete lining over the crown. Yielding Swellex was installed to counter expected problems of rockburst, caused by the increased overburden in competent gneiss. In rockburst, the pressure builds up in the rock around the tunnel perimeter, and can yield explosively, causing dangerous spalling. If the rockbolt is designed to take up some of this swelling pressure, then the bursting effect can be mitigated without compromising on support. Experience gained at Raron has been used to develop the new Swellex Manganese Line, which offers more loading capacity and enhanced elongation. COP 1432 rock drills speeded up the drilling, and the easy and fast installation of the Swellex bolts provided immediate support behind the TBM. The TBMs advanced an average of around 90 m/week. ROCK & SOIL REINFORCEMENT

Rocket Boomer L2 C in top heading at El Fabar.

Projects: Gotthard base tunnel, 57 km; Lotschberg base tunnel, 34 km. Location: Switzerland Excavation method: Drill/blast, full section and top heading; TBM 9.43 m diameter. Contractors: Satco jv (Mitholz), MaTrans jv (Raron), AstHolzmann (Amsteg). Designers: Consortium of best Swiss engineering and consulting companies. Rock: Mainly hard rock such as granite, limestone, schist, gneiss, granodiorite, amphibolite. Rock reinforcement requirement: Safety; versatility to cope with geology and load requirements; high productivity with drill/blast and TBM; some rock bolts have to withstand rock bursts. Rockbolts selected: Standard Swellex, Super Swellex, Yielding Super Swellex. Operations in the north were concentrated at the lateral adit at Mitholz, from where two faces were driven south, and one north, using Atlas Copco Rocket Boomer XL3 C three-boom rigs. These are each followed by a suspended trailing backup carrying transformers, cable reels, ventilation fans and ancillary equipment. A full 8 m-wide x 8.5 m-high face was drilled to 4.5 m depth for each blast. During and after mucking out, the blasted area was mechanically scaled, and the roof and sides were shotcreted. Some 20-30 Swellex 3 m or 4 m rockbolts were then installed into holes 85

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Mountain of Swellex at Mitholz on AlpTransit Lotschberg.

Atlas Copco Rocket Boomer XL3 C, one of three delivered to Mitholz.

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drilled by the Boomer XL3 C. In squeezing ground, wire mesh and fibre reinforced shotcrete were used, and, in the extreme south of the drive, where crystalline rock may produce rockbursts, Swellex Manganese and MAI SDA were used.

At Alptransit Gotthard, contractor Ast Holzmann completed the 1.78 km Amsteg access adit on a 1% downgrade through the Aar Massiv and Erstfeld gneiss to the main tunnel horizon, where four faces were established. An Atlas Copco Rocket Boomer 353E drillrig was used on the adit to drill a full face of 105-110 holes to an average 3.5 m depth. The face took around 1 h 50 min to drill out, and the holes were charged with aluminized slurry with non-electric detonation. Average daily advance was 10 m, or four rounds. Swellex rockbolts of lengths 3 m or 4 m were installed into holes drilled by the Boomer 353E, using the rig basket for access. Following each second round of advance, a 5 cm layer of shotcrete was applied to the roof. A further 5 cm of fibrereinforced shotcrete was then applied to the walls, and another 2 cm to the roof. At the base of the adit, a 90 m-long x 13 m-wide x 12.5 m-high transformer room was excavated, again using the Rocket Boomer. This was advanced as an 8.5 m-high top heading and 4 m bench to create a 125 sq m cross-section, reducing to 108 sq m at the back. Most of the support was by 3 m and 4 m-long Swellex set in 38 mm holes. The junction with the running tunnels is hugely impressive, particularly in view of the 1,000 m of overburden at this point. The profile of the running tunnels was near perfect, with average overbreak of 18-22 cm measured by the Bever profiler on the drillrig. Two 9.58 m TBMs started on the 11.4 km drives towards Sedrun in mid2003, with 40 m-long crosspassages at 320 m intervals. In the opposite direction, excavation towards the portals has not yet started. Meantime, Murer and Strabag have driven a 1.88 km-long cable tunnel between the transformer room and the existing Amsteg power station using a Robbins 3.7 m-diameter hardrock TBM. Swellex has a prominent role in AlpTransit, since Swiss designers can rely on the safety and controllability of its installation, as well as its versatility, which is particularly important in long and deep tunnels. Contractors are happy that Swellex is a good investment, improving productivity and helping to keep costs under control. ■ ROCK & SOIL REINFORCEMENT

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Rapid Support Behind the TBM Improving Utilization For TBM tunnelling, the Alpine and Appenninic geology of Italy is both good and bad. The relatively hard rock suits TBM tunnelling, but volcanic and seismic activity over the millennia has rendered it highly fractured and disturbed, requiring a relatively high degree of support. TBM utilization in Italy can be as low as 30% to 50%, with rock support and reinforcement accounting for 50%, or more, of the total production time. When rock support is required in conjunction with a TBM operation, consideration must be given to the type of support required, and how quickly it can be installed. In highly fractured rock, reinforcement, principally rockbolts, should be installed as quickly, and as close to the face, as possible. However, for most types of TBM, installing support close to the face results in downtime. Given the relatively high cost/m of TBM tunnelling, such stoppages are a major concern for both the contractor and the client. Developments in the speed and ease with which support can be applied to improve TBM utilization are of interest to all parties involved in TBM tunnelling in disturbed rock. The main challenge is to limit machine downtime and increase productivity while at all times respecting safety requirements. At Alassio, the client specified Swellex and supplied a stock of bolts to the contractor, such was the interest in improving TBM utilization.

Project: Pilot tunnel for motorway link road. Location: Alassio, Italy. Excavation method: Open face TBM. Contractor: Ilbau srl. Rock: Soft, dry, non-abrasive calacareous marls, some clay and blocky rocks. Rock reinforcement required: Fast, dependable roof support with five-year life. Rockbolt selected: Swellex.

Alassio Motorway Link Road Ilbau, a division of Austrian contractor Strabag, has excavated a total of over 100 km of TBM tunnels, of which more than 50 km are in Italy. The company employed its veteran 3.6 m-diameter Jarva Mk12 TBM to excavate the pilot for the 2.4 km-long two-lane road tunnel on a new link road between Alassio and the nearby Genoa-Firenze motorway. The four-lane highway was built in the 1960s, and passes through many tunnels and over many bridges on its route parallel with the Italian coast. As with all TBM projects, the aim at Alassio was to install adequate support with minimum impact on TBM productivity. With a stroke of 1.2 m and a cutterhead body of about 2 m, the Jarva TBM allowed installation of immediate support within 3 m of the face. However, since this involved TBM downtime, it was kept to a minimum, with most support work carried out concurrent with TBM advance from the platform on the trailing backup some 16 m back. This also allowed installation of truly radial rockbolts in the crown.

Ground support by rock classification behind a TBM.

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Table 1. Comparison of rock classifications methods. Class

I II III IV V

Bieniawski 1973 RMR

Deere 1969 RQD

83 67 52 29 15

90 75-90 50-90 25-50 less than 25

Barton 1974 O-Norm Q Class (3.9 m dia. TBM) 33.0 12.5 8.5 1.5 0.09

F1-F2 F3 F4 F5 F6

As part of its contract, Ilbau was responsible for the design of the pilot tunnel support. For more reliable estimating, and easier communication with its client, Ilbau developed a rock class and support measurement system specifically for TBM tunnelling (Table 1). Adapted from established Austrian practice, the table not only considers the most appropriate rock support for given rock conditions, but also specifies where, and how quickly, the support should be installed. In better rock conditions (Classes F1, F2 and F3) bolts, mesh and shotcrete could be installed from the working platform without interrupting TBM progress. In Classes F4, F5 and F6, support must be installed as close to the face as possible, and requires a halt in TBM advance. Class F7 constitutes rock with no selfsupporting capacity. In such conditions, ground consolidation techniques, or full lining support with ribs and timber lagging or bolted liner plates, may be required. In zones of extremely difficult ground, consolidation and support measures ahead of the TBM should be considered. At Alassio, because of the potential impact on TBM utilization, the payment schedule for rockbolting and other support requirements varied according to where it was installed, with higher unit prices for support installed close to the face, involving TBM downtime. The client specified the use of Swellex for rock reinforcement at Alassio, and supplied the requisite bolts to Ilbau for installation. Although sometimes perceived as more expensive than alternative rock support and reinforcement systems, the unit price of Swellex becomes substantially less significant when compared with the costs saved in labour and TBM downtime. The easy handling of Swellex is welcomed by tunnelling crews, and its geomechanical properties and speed of installation are attractive to consulting engineers, clients and contractors. Alassio geology comprises mainly soft, dry, non-abrasive calcareous marls with 88

defined bedding, some clay content, and zones of fractured and blocky rock. Rock quality tends to change very rapidly, and often from stroke to stroke of the TBM. As a rock reinforcing tool, Swellex is effective over a particularly wide range of rock and soil types. In Ilbau’s table of rock support for instance, Swellex is applicable in all classes requiring rock bolts, from class F1 to F6. By specifying Swellex, there is no need to keep a stock of any other type of bolt on site. Together with its ease of application and immediate support potential, Swellex has the all-round advantage. In the first 1,918 m of the Alassio pilot tunnel, required support was mostly that of types F2 to F4, with 15% in type F5. Swellex reinforcement over the same length averaged about four bolts/linear metre, 60% of which were 1.5 m-long, and the remainder 2.1 m. Support installed was about 10% more than originally estimated, with a corresponding 10% reduction in productivity. Swellex, wire mesh and shotcrete were used in fault zones where roof falls had occurred. In other areas, thin layers of shotcrete spalled off, with small falls of rock away from bedding planes. These created no serious safety hazards, and confirmed that Ilbau was installing adequate support for a pilot tunnel, neither too much, nor too little. Rock support accounted for approximately 50% of TBM downtime on the Alassio pilot tunnel, with most falling into support types F2 to F4, and 15% in type F5. To monitor the quantity and quality of support installed, the client’s consultant geologist visited the site about twice a week. In addition, the consultant monitored geotechnical instrumentation installed by Ilbau. Along the tunnel there were 15 convergence measuring stations, and three stations containing three groups of 1.5 m, 3 m, and 4.5 m long extensometers in the crown and into each wall, as well as five tangential and five radial pressure cells. Data gathered greatly assisted the main tunnel final support and lining designs. The TBM completed the 2,472 m-long pilot tunnel in eight months, working 127 h/week on a 2 x 11 h shift/day, 5.5 days/week, and broke through on schedule. Average advance was about 15 m/day, with a best advance of 53 m/day in class 2 rock, installing 110 bolts, mainly from the backup platform. This was close to the optimum 60 m/day achievable in a short tunnel operating a single track muck hauling system. ROCK & SOIL REINFORCEMENT

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Val d’Arzino Water Diversion The Val d’Arzino is north of Venice, near the border with Slovenia and Austria. A scheme to divert water from Arzino River to the city of Pordenone included a tunnel, 5.7 km long, 4.5 m diameter, with a slope inclination of 1.5% to 2%, mostly through stable limestone and marl strata. The older formations overthrust the younger strata, and the tunnel crosses the main fault zone. The area is highly seismic, and, in 1976, a major earthquake with epicentre near the Val d’Arzino was apparently linked to the faults crossed by the tunnel. The rock encountered along the tunnel alignment demonstrated a large variation in stability. A large section of the tunnel (63%) was driven through good, fair or fairly unstable rock (Class Fl to F3), but the remainder was through difficult, unstable ground (Class F4 to F6). The weak formations include rocks such as marl, mudstone and claystone, with faults, overthrusts, and weathered rock close to the surface or affected by underground water. The challenge was to select a machine with high productivity in good rock, but which would still be able to overcome difficulties in weak and unstable rock. The contractor, Ilbau, used a brand new Robbins TBM, with Swellex rockbolts as support. Average advance rate was 20.9 m/day and 453 m/month, and highest advance rate was 90 m/day and 808 m/month. TBM utilization varied from a maximum of 45% in Class Fl to a minimum of 8.5% in Class F6, averaging 25.6%. The penetration rate was between 5.5 m/h in Class Fl and 3.5 in Class F5. Rock reinforcement took 44.4% of the total time. The contractor worked 2 shifts/day, 11 hours/shift. Best performance was 54 m/day in Class Fl, but a significant achievement was 7.4 m/day in Class F6, where heavy rock reinforcement was required, and only 2 m to 4 m/day would be expected. It is interesting to note that the good overall performance was achieved in spite of two poor months of around 50 m/month. A delay was caused by an unexpected methane gas inflow emanating from a black marl formation, which accumulated close to the machine and caused an explosion. Luckily nobody was injured, but tunnelling stopped for three weeks to upgrade gas detection, install safety devices, and improve ventilation systems. ROCK & SOIL REINFORCEMENT

Project: Water diversion tunnel. Location: Arzino River, Pordenone, Italy. Excavation method: Robbins 4.5 m-diameter TBM. Contractor: Ilbau, Austria. Rock: Limestone and marl, interspersed with mudstone, claystone and weathered formations. Rock reinforcement required: Rapid support behind TBM in variable strata. Rockbolt selected: Swellex.

Effect of rock conditions on the 4.5 m TBM at Val d’Arzino.

Rock class distribution at Alassio.

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Project: Underground sewage treatment plant and tunnels. Location: Media Pusteria valley, Alto Adige, Italy. Excavation methods: 3.9 m-diameter TBM, drill/blast. Contractor: Ilbau srl. Rock: Alpine schist. Rock reinforcement required: 3 m and 4.5 m bolts for pilot tunnel and cavern support. Rockbolts selected: Standard Swellex, Super Swellex.

Alto Adige Treatment Plant The Alto Adige area of the Italian Alps is a paradise of mountains, valleys and rivers, where protection of the environment is of paramount importance, especially as the local economy relies heavily on tourism. This was uppermost in the minds of planners when a sewage treatment plant became an urgent necessity in the Media Pusteria valley, near the Austrian border. Rather than upset the environmentalists, they opted to place the 25,000 sq m plant underground. This plant is the first of its kind in central Europe, and will serve 95,000 people, cleaning 95% of phosphorus, nitrogen and other oxygen-depleting pollution out of the waste water. The plant will occupy the smallest possible surface area at the bottom of the valley, eliminating odour and noise, and will also be safer in the event of earthquakes. The design and size are in accordance with the latest European regulations, and will achieve strict purification limits. TBM usage statistics for different rock types. Relation between Classification, ROP and TBM Utilization Rock

ROP (m/h)

Utilization %

Daily average (m/day)

Thrust (bar)

Cutter load (t/cutter)

Torque (amps)

J1

4.61

35.2

35.7

99.5

14.3

125

J2

5.88

38.0

49.2

82.7

11.9

138

J3

3.96

47.1

41.0

93.1

13.4

137

T1

4.71

46.6

48.3

86.9

12.5

133

R

7.70

25.6

43.3

73.7

10.6

144

LT

5.27

19.9

23.1

56.1

8.1

114

F

5.22

21.4

24.5

62.4

9.0

130

CF

5.28

38.4

44.6

76.2

10.9

128

J1 to LT are volcanic rocks-pyroclastites. F and CF are Brixen quartz-phyllites.

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Alto Adige was a pilot project for Italy as a whole, with a view to building other facilities such as reservoirs, storage depots, car parks and sport and recreational facilities underground. The plant consists of a 950 m-long, 3.9 m-diameter headrace tunnel, which conveys the sewage into large caverns where screening, desanding, degreasing, preliminary sedimentation, biological and chemical treatment, are carried out. Some of the resulting sludge is processed for agricultural applications, and some is converted into biological gas to feed a built-in heating plant, achieving a 50% saving in energy costs. The headrace tunnel and 326 m-long pilot tunnel for the central cavern were driven by an Atlas Copco Jarva Mk12 TBM. Standard Swellex bolts were used for reinforcement in the pilot tunnel, and more than 4,000 Super Swellex in 3 m and 4.5 m lengths were used for reinforcement of the central and side caverns. Blasthole drilling was carried out by an Atlas Copco Boomer H 188 two-boom rig, equipped with service platform. In the drilling and bolting operations, Atlas Copco Secoroc rock tools were used throughout, drilling 51 mm and 64 mm holes. Bolting, using both Super Swellex and cable bolts, was carried out with an Atlas Copco rig equipped with a BUT 35 boom and automatic rod adding system. A service contract provided for regular maintenance of the COP rockdrills, which were dispatched to the Atlas Copco workshop in Milan after every 5,000 drillmetres. Above ground, an Atlas Copco ROC 612HC with folding boom was used for benching on the construction site where the administration and service buildings were erected. The site manager found it a great benefit to have a single supplier covering the job, for drillrigs, rock drilling tools, and rock reinforcement. In addition, where drilling long holes for bolting in a narrow space is normally difficult, the rod adding system on the BUT 35 boom made it easy. The geologist found that the Swellex bolts fulfilled their safety function excellently in the schist rock. They were fast to install and gave immediate rock support. ■ ROCK & SOIL REINFORCEMENT

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Swellex in Large Hydroelectric Projects Construction Reliability International consultants are increasingly specifying Swellex in their designs for hydro projects, because of the need for absolute controllability of installation. Unlike railway and highway tunnels, hydro tunnels are not easy to inspect, so there has to be a greater emphasis on reliability of construction methods and materials. The fact that projects can be designed in one country for construction in another, using materials from a variety of sources, can be a cause of great concern to both the hydro tunnel designer and his client. Using Swellex as the specified support system reassures both parties that the quality, flexibility and reliability factors are fully covered.

Project: San Roque on Agno River, 345 MW. Location: Philippines. Excavation method: Drill/blast. Contractor: Raytheon Ebasco Overseas Limited. Designer: Golder Associates. Rock: Mainly volcanic tuff. Rock reinforcement requirement: Quality control, capacity to work in soft and weak rock. Rockbolt selected: Super Swellex.

Removing the Bottleneck at San Roque US contractor Raytheon Ebasco Overseas Ltd. (REOL) was responsible for the San Roque dam project on the River Agno in the Cordillera Mountains of Pangasinan province, about 250 km north of Manila, the Philippines capital. The 1,100 m-long, 188 m-high dam embankment is believed to be the biggest in Asia, and is the twelfth largest in the world. It will create a vast 14 sq km reservoir for recreation, provide downstream irrigation to 87 sq km of farmland, and supply power to the national grid from the dam’s integral 345MW hydroelectric power station. Three diversion tunnels were designed to accommodate a flood flow of 4,600 cu m/sec. The two largest high-level tunnels are 16.5 m-high, 11 m-wide and horseshoeshaped. They will each cater to flows up to 2,100 cu m/sec. The remaining 400 cu m/sec of flood water will go through the smallest low-level tunnel, which is 817 m-long, 6 m x 6 m, and also horseshoe-shaped. It will normally have a flow of about 120 cu m/sec. The underground fleet at San Roque comprised 22 Atlas Copco Wagner Scooptram loaders and Mine Trucks, the ROCK & SOIL REINFORCEMENT

first such equipment to be used in the Philippines. Six ST-7.5Z loaders worked on the main tunnels, matched by the same number of MT-436B mine trucks. These were supported by a further ten of the smaller Wagner ST-2D units for use in the dam’s grout gallery tunnels. When the size of the tunnels was increased, six of the Wagner ST-2D loaders were replaced with the larger Wagner ST-3.5 units. Exceptional availability of between 92% and 96% was achieved, exceeding the 85% guaranteed by Atlas Copco. Atlas Copco Wagner’s comprehensive preventative maintenance programme, combined with operative training, which is part of the company’s on-site full service package, was the key to the equipment’s success.

Three diversion tunnel portals at San Roque.

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Installing Super Swellex at San Roque.

Super Swellex was specified by the designer, Golder Associates of Georgia, US, as the regular pattern bolt. This hydraulically-expanded bolt gives immediate rock support and full column bond, and has an excellent quality control procedure during its installation. An average advance

Economical Support Solution at Uri Atlas Copco Boomer H178 face drilling at Uri hydro scheme.

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The Uri project is located in the foothills of the Himalayas, in the Kashmir Valley of northern India. The new hydropower plant

of 7 m/day was achieved on each face, generally from two 4 m rounds. After drilling, blasting and mucking out, the exposed rock was sprayed with 50-75 mm of fibre-reinforced shotcrete before installation of the 4 m-long Super Swellex bolts. A second application of shotcrete was then applied to produce a smooth 350 mm-thick tunnel lining. Immediate rock support was especially important when facing the soft and unstable rock at San Roque. Moreover, in such rock conditions, reinforcement is a bottleneck in the excavation cycle, so the contractor was pleased with the opportunity to use a fast and trouble-free bolt like Swellex to speed up production. The 11 m-wide, 8 m-high benches remaining in the two large tunnels were duly excavated on schedule before the start of the typhoon season. The Atlas Copco Wagner fleet then moved on to muck out two 1,500 m-long tunnels at the site, a 7 m-diameter irrigation tunnel and a 9 mdiameter tunnel to the main powerhouse. San Roque Power Corporation will sell and supply electricity to the national grid from 2002 for 25 years, before transferring ownership to the Philippines National Power Corporation.

will harness the flow of the Jhelum river, and its 480 MW turbines will supply much-needed electricity to the region. Urico contractors, a design/construct joint venture led by Skanska and NCC, employed six Atlas Copco Boomer H178 drillrigs on the development of 22 km of tunnels at Uri. The Boomer H178, with its three booms, was selected as the most flexible machine available to excavate faces of cross-sections between 25 and 100 sq m, together with the 22 m-wide machine hall cavern. Average progress in the tunnels was 250 m/week, with a best week of 278 m. Atlas Copco assisted the contractors with an extensive training programme to teach the local employees how to operate the rigs. Rock reinforcement at Uri consisted of shotcreting and bolting, with Swellex comprising 75% of the bolts used. The drillrigs were used for all rockbolting work, installing 700 x 3 m-long bolts/week. Swellex was chosen wherever possible, because they are quicker to install, and more economical overall, than grouted ROCK & SOIL REINFORCEMENT

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rebar bolts. Indeed, in places where water was flowing, Swellex was the only realistic option. The rock encountered varied from quartz schist to shale, with some of more recent volcanic origin. Construction at Uri involved the excavation of 1.2 million cu m of rock underground, and the placement of 375,000 cu m of concrete lining along the 15 km of water tunnels.

Right Combination at Alto Lindoso Atlas Copco was the main supplier to Italian contractor Torno for the Alto Lindoso 600 MW underground hydroelectric plant located in northern Portugal, close to the border with Spain. The company provided all of the drilling equipment needed for 12 km of headrace, tailrace and access tunnels. The power generating plant was installed in a chamber 70 m south of a 110 m-high arched dam with a span of 296 m near the confluence of the Castro Laboreiro and Lima rivers, which provides a maximum head of 338 m. Atlas Copco helped train the drillrig operators and maintenance personnel, and provided a manned workshop container for hydraulic service operations at site. The five Boomer rigs employed drilled mainly in hard granite with a compressive strength of between 1,800 and 2,000 bar. Around the tailrace tunnel exits, the

Project: Uri hydroelectric power station. Location: Northern India, Jammu and Kashmir. Excavation method: Drill/blast, top heading and bench. Contractor: Joint venture Skanska and NCC. Designer: Skanska/NCC. Rock: Variable, from weak to hard rock. Rock reinforcement requirement: To cut bottleneck in production cycle. Rockbolt selected: Standard Swellex.

Project: Alto Lindoso hydropower. Location: Northern Portugal, close to Spanish border. Excavation method: Drill/blast. Contractor: Torno Construction. Client: EDP – Portugal National Power Board. Rock: Hard granite, weathered granite, schists, and shales. Rock reinforcement requirement: To provide temporary support for access ramps, tunnel and chambers. Rockbolt selected: Standard Swellex. drillers faced weathered granite, as well as some schists and shales. Torno operated a two-shift system of 12 h/shift, gaining advances of 3.5 m/round. Swellex rockbolts were used exclusively for rock reinforcement, complemented where necessary by shotcreting, wire mesh and steel arches. The combination of Torno skills with Atlas Copco service succeeded in completion of what had previously been a very troublesome project, and Alto Lindoso is now contributing power to the Portuguese national grid.

View of dam site at Alto Lindoso.

ROCK & SOIL REINFORCEMENT

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Project: 40 m-deep open pit at Ybbs-Persenbeug power station. Location: River Danube, Austria. Excavation method: Hydraulic breakers and excavators. Contractor: JV of Mayreder-Kraus, Porr, Universale, Hofmann Maculan, Stuag, Ilbau, Strabag. Rock: Faulted bedrock. Rock reinforcement required: To secure vertical faces of open pit. Rockbolt selected: Super Swellex up to 12 m-long.

Super Bolts on the Danube The River Danube drives turbines in no less than nine power stations as it wends its way through Austria. The oldest, at Ybbs-Persenbeug, was built in 1959 with General view of open pit at YbbsPersenbeug power station.

six turbines installed. By the early 1990s, more capacity was required, and it was decided to install an additional 48 MW turbine. The project involved the excavation of a 180 m-long x 40 m-deep x 20 m-wide open pit alongside the existing station, without interrupting its operation. Trials with drill/blast indicated an unacceptable high level of vibration which, combined with faulting in the bedrock in the vicinity of the station, threatened the existing turbine installations. It was decided to use hydraulic breakers and excavators, together with additional rock reinforcement of the vertical walls of the pit. The design consultants advised the client that cement-grouted rockbolts, which take up to a week to set, would cause excessive delays to the project. Accordingly, it was decided to use Atlas Copco Super Swellex bolts which, even in the long lengths required in this unusual installation, take only 15-20 minutes to install, including the time spent drilling. Bolts of lengths 8 m, 10 m, and 12 m were guided into the 48 mm-diameter drillholes by hand, and then pushed home by one of the two Atlas Copco drillrigs employed at site. Some 2,000 Super Swellex bolts were used, 900 of which were 12 m-long. The bolts gave instant support to the walls of the pit, helping keep the project on time and within budget. The chief engineer of the joint venture constructing the power station observed that it would have been impossible to stick to the construction schedule without the rapid and secure installation offered by the Swellex bolting system.

Inserting 12 m-long Swellex rockbolt to support the cut beside the Danube.

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Rock Mass Stabilization at Tala Hydro Tala Hydro scheme has been constructed in the remote Himalayan kingdom of Bhutan, using more than 40 items of capital equipment supplied by Atlas Copco. The dam site is about 85 km by road from the border with India, and is located near the village of Wangkha, on the Wangchu river, some 3km downstream of the existing Chukha tailrace outfall. Hindustan Construction found MAI anchors were crucial for stabilization of the walls of the desilting chambers at Tala, and as primary support during excavation of the Head Race Tunnel (HRT). The same anchors have also been found to be very useful in reducing pore water pressure behind the support system. Major features of Tala are: three desilting chambers sized at 250 m x 13.9 m x 18.5 m; a 22.97 km-long, 6.8 m finished diameter, 50 sq m modified horseshoeshaped, concrete-lined headrace tunnel (HRT); and an underground powerhouse 206 m-long by 19 m-wide and 45.5 mhigh, with transformer cavern 191 m-long by 16 m-wide and 27 mhigh. The HRT, which has been excavated at 7.5 m-diameter with rock cover of 60 m to 1 km, utilized five construction adits. In the tunnels, Atlas Copco Boomer 352s were used in rock classes 1, 2 and 3, where the average advance was 120 m/month, and in class 4 rock up to 70 m/month. Class 5 rock, which had to be fully ribbed at 60-75 cm intervals, strutted, bolted, meshed and shotcreted, slowed advances to 30 m/month. The Atlas Copco Secoroc button bits were reported by the contractors to have S.D. Jeur, Project manager, Hindustan Construction Company, C4 Package used Atlas Copco Odex for piperoofing, in combination with MAI SDAs, to make tunnelling possible through soil.

ROCK & SOIL REINFORCEMENT

Project: Tala Hydro on Wangchu river, 1,020 MW. Client: Tala Hydro Power Authority (THPA). Location: Wangka, Kingdom of Bhutan. Excavation method: Drill/blast. Contractors: Jaiprakash; Hindustan Construction; Larsen & Toubro. Rock: Gneiss with quartzite bands and biotite schists. Rock reinforcement requirement: Roof support. Rockbolt selected: MAI SDA. achieved up to 30% longer life than expected. Hindustan Construction used MAI self drilling anchors (SDA) for stabilizing the reinforced concrete wall of desilting Chamber No 3. The wall of the chamber was anchored to the deeper competent rock using one row of 114 MAI SDA with 20 m length and 38 mm-diameter at 3 m centres, and another row of 36 MAI SDA with 24 m length and 51 mm-diameter at 3 m centres. 32 t pull out tests conducted on the 38 mm-diameter and 20 m-long MAI SDA resulted in displacements of 11 mm and 17 mm respectively, well within specification. Hindustan Construction used the Drainage, Reinforcement, Excavation, Support Solution (DRESS) in the 330mlong section of HRT affected by adverse geology in Package C4. Here, MAI SDAs were used both as radial bolts and as drainage elements, in combination with Odex Piperoofs. For anchoring steel arches, SDA of 8-12 m lengths were installed in a systematic pattern. If no water seepage resulted, they were grouted. Two 38 t pull out tests were conducted on 38 mm-diameter, 8 m-long MAI anchors to check the efficacy of grouted anchors in the poor strata in the HRT. These passed, with displacements of 16 mm and 22.8 mm.■

Atlas Copco Boltec 435H at work in Tala headrace tunnel.

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Top Combinations in Japan Speed with Safety Tunnelling operations in Japan are to the highest standards of quality and safety, and Swellex was originally introduced as a problem solver in specific rock conditions such as high water inflow and squeezing ground. Since then, Swellex has been used to replace steel arches on a number of projects, to good effect. Experience obtained on the more difficult projects has led to Swellex being specified as a pattern bolt in current projects, mainly where grouted rebars are considered too slow to install and take load. Wherever there is rapid deformation of the strata, Swellex is the bolt of first choice because of its fast installation and immediate load bearing characteristics. In Japan, it is a popular combination of speed with safety, controllability and reliability.

Project: High Speed Railway, Daini Shibishan. Location: Kyushu Island, Southern Japan. Excavation method: Drill/blast. Contractor: Kajima-Zenitaka-Shita joint venture. Project Owner: JR – Japan Railways. Rock: Weak formation of shale, sandstone and clay strata. Rock reinforcement requirement: Versatility to cope with geology, immediate rock support, non sensitive to water inflow. Rockbolts selected: Super Swellex, Midi Swellex.

Bullet Train Secured on Kyushu Daini Shibisan is a twin-track railway tunnel, part of the high-speed railway system under construction between Kagoshima and Kumamoto on the large island of Kyushu, south of the Japanese mainland. The 3,394 m-long tunnel, one of thirteen in the section, was excavated by the Kajima-Zenitaka-Shita joint venture, who had to overcome major problems with the amount of groundwater present in the sandstone, shale and clay strata. Drilling and reinforcement was complicated, with some holes collapsing as soon as they were drilled, making it virtually impossible to inject the cement required to grout rockbolts. The solution was Atlas Copco Swellex rockbolts, which expand to fill the hole, need no cement, and have the advantage of providing immediate reinforcement to the surrounding rock. Atlas Copco Boomer drifting rigs installed the bolts, which were expanded using an ESPA51 electric Swellex pump. In this type of environment, Swellex bolts are known to perform much better than conventional bolts, and are also more cost-effective. Their introduction into Daini Shibisan tunnel ended the expensive ROCK & SOIL REINFORCEMENT

business of having to re-excavate rock when it had been deformed by lesseffective reinforcement methods. The site manager described the Swellex contribution to the operation as highly valuable, and an extremely efficient and reliable method of dealing with the porous and highly-fractured rock formation.

Portal at the Daini Shibisan high speed railway tunnel.

Installing Swellex rockbolts at the Daini Shibisan face.

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Project: Chou Highway, Shin-Iwatono tunnel. Location: Honshu Island, Central Japan. Designers: JH, Japan Highways. Excavation method: Roadheader, drill/blast. Contractor: Tobishima/Aisawa joint venture. Rock: Variable volcanic formation including andesite, tuff and breccias. Rock reinforcement requirement: Safety, versatility to cope with geology, even in soft layers. Rockbolt selected: Super Swellex, Midi Swellex.

Project: Sobu road tunnel. Location: Honshu Island, Central Japan. Excavation method: Drill/blast, microbenching. Rock: Mixture of sedimentary and volcanic rock formations. Rock reinforcement requirement: Safety, versatility to cope with geology, even in soft layers. Rockbolt selected: Super Swellex, Midi Swellex.

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Easily Through Difficulties on Honshu The Chuo Highway connects Tokyo and Nagoya in central Japan, and work is under way to widen the road from two to three lanes. Shin-Iwatono is one of the tunnels excavated along the alignment, and is located 100 km north west of the capital. Work on the 1,591 m-long tunnel, with its cross-section of 130 sq m, was carried out by the Tobishima/Aisawa joint venture for Japan’s Public Highway Corporation. Rock at the site is andesite lava and tuffbreccia. The first 126 m of tunnel excavation was by roadheader in soft tuff-breccia. Drilland-blast operations then commenced in andesite lava using an Atlas Copco Rocket Boomer 352-2B, the first in Japan, and leased by local distributor Drill Machine. The Rocket Boomer 352-2B is equipped with two BUT 35 booms, with COP 1838 rock drills mounted on BMH 6812 feeds. Advance per round was 1.2 m, with penetration

Solving a Geological Puzzle with Swellex At the 3,692 m-long Sobu tunnel located in mountainous terrain on the road between Kyoto and Yonago Tottori prefecture, top performance was achieved by COP 1838 rock drills fitted to a Rocket Boomer H 195. The cross-section at Sobu is between 90 and 100 sq m, and excavation was by micro-benching, a common method in Japan. The rock is sandstone, shale, tuff and porphyrite, with a compressive strength of 400-500 bar. The drillrig achieved 100 holes in 40-50 minutes, with a penetration rate of 3 m/min, and total advance was 6 m/day. Site management reported low consumption of shank adapters and other accessories. Japanese tunnels require the highest standards in safety and support, and the quality of rockbolts, and their standard of installation, are paramount. Initially, in Japan, Swellex bolts were employed as a problem solver for specific rock conditions, such as squeezing ground and high water inflow. They have also been used in difficult situations to replace steel arches. Lately, large quantities of

rates of 2.5 m/min in the tuff-brecchia, and 3.0 m/min in the harder andesite. Swellex rockbolts were selected because of their versatility and effectiveness in the varying ground conditions, and the speed with which they could be installed. These properties were particularly important in the softer strata mined by the roadheader.

Rocket Boomer 352-2B rockbolting at Shin-Iwatono highway tunnel.

Swellex bolts have been employed in pattern bolting on a number of projects in heavy and fast deforming ground, where grouted rebars are considered too slow to take load. There is also increasing acceptance of Atlas Copco MAI SDA self drilling rockbolts. ■

Rocket Boomer H 195 micro-benching at Sobu road tunnel.

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Front Stabilization Using MAI Anchors Improving Rock Quality Drilling ahead of the tunnel face and installing bolts or grout is a common way of improving rock quality before actual excavation takes place. Atlas Copco has, as a supplier, been involved in a number of such projects, both in mining and construction. Pre-reinforcement is a different way of approaching ground control. Instead of relying on supporting the ground following excavation, prereinforcement increases rock strength prior to excavation. There are several benefits to this. First, a pre-reinforced rock mass will be less damaged by blasting, and less disturbed by elastic and non-elastic stress redistribution around the excavation. Second, the rock mass is never without support, even at the split second following blasting of the round. Third, the support can be more active when installed early, rather than passive when installed later. Fourth, pre-reinforced ground will not deteriorate or collapse as rapidly as a totally unsupported excavation, allowing a safe working period for installation of regular support. In tunnelling, the umbrella grouting method of pre-reinforcement is frequently used. This method presupports the planned roof area with steel rods. Large holes are drilled in the future roof perimeter, and grouted at high pressure with high strength, fine grained cement grout. Through each cemented hole, a smaller hole is then drilled, in which a high-strength reinforcement bar is grouted. Although highly effective for shallow tunnels driven in very adverse ground conditions, it is easy to see that such a work-intensive operation would be deemed neither practical nor economic for mining applications, although the underlying concept could definitely be useful.

ROCK & SOIL REINFORCEMENT

Project: Mineral conveyor tunnel 9.36 km-long with 4.5 m-diameter. Location: Pontida Valley, Italy. Excavation method: Open gripper TBM. Contractor: Strabag Del Favero. Rock: Flysch and micaceous sandstones with silts and clay layers. Rock reinforcement required: Umbrella of 24 x 9 m-long bolts. Rockbolt selected: Atlas Copco MAI Self Drilling Anchors.

Umbrella System at Montegiglio

Umbrella of 24 MAI SDA type R51L at Montegiglio.

Montegiglio tunnel, in Italy, is a 9.36 kmlong, 4.5 m-diameter connection intended to support the mineral extraction activity of Colle Pedrino and Montegiglio quarries. A conveyor belt for the movement of mineral to the Calusco d’Adda cement plant is installed in the tunnel. From the south entrance of Montegiglio quarry, a cableway to Pontida valley links the two quarries. The tunnel was driven by TBM on a different alignment, westward and more northerly. For the first 800 m, the tunnel proceeded straight on a SW-NE heading beneath Carvico village at a downward slope of 11.4%. The TBM was 99

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BSH 110-SDA for handling MAI anchor.

operated 5 days/week in three 8 h shifts/day, with maintenance carried out during the morning shift. Every 200 m of advance, the TBM had to be stopped for a shift to extend the conveyor belt. The conveyor belt storage was located in the area in front of the south entrance. The stabilization and support interventions for the Montegiglio tunnel depended upon the observed geological and geotechnical conditions of the rock. Six types were defined, ranging from non-systematic intervention, to bolts with increasing thickness of shotcrete, up to bolts with net, ribs and reinforced shotcrete. During the initial excavation in the Flysch di Bergamo geology, contractor Strabag Del Favero suspected weak ground conditions ahead, and performed a horizontal

Project: Twin-tube 5 km-long highway tunnel. Location: Hanbau-Tsaotwen Expressway, Taiwan. Excavation method: NATM with top heading, bench and invert. Consultant: China Engineering Consultants Inc. Rock: Gravel with mudstone and clay alternations. Rock reinforcement required: Presupport around arch and sidewalls, roof support. Rockbolt selected: Atlas Copco cement grouted SDA.

Presupport at Pakuashan The 5 km-long Pakuashan tunnel is being constructed over a seven-year period in Central Taiwan, as part of the HanbauTsaotwen Expressway, one of 12 planned east-west connections. NATM is being used, despite the poor geological conditions, which do not fit any of the commonly used rock classifications. 100

investigation along the axis of the tunnel. The results showed that further advance with the TBM would achieve only limited results. In fact, at that point, the excavation met micaceous sandstones, with silts and clay layers with the consistency of damp sand. These exhibited very low cohesion, or no cohesion at all, due to the weak grain bond. In these conditions, excavation became difficult, with some collapse of material from the crown. The support design for this particular type of section specified an umbrella of steel pipes with diameter 104 mm, with a length of 12 m and 3 m overlap. Due to the small tunnel diameter of 4.5 m, only limited space was available for positioning and working the drilling equipment, so an alternative solution was needed. Atlas Copco proposed the use of a Boomer H145 equipped with two booms and COP 1440 rock drills. The feed length was adapted to 4.4 m to suit the tunnel diameter, to enable Strabag Del Favero to install radial anchors. More importantly, an umbrella could be installed consisting of 24 Atlas Copco MAI SDA of type R51L, with a length of 9 m and a overlap of 3 m. This allowed the contractor to excavate a total of 6 m, in steps of 1 m, before placing the next umbrella. After some initial mechanical adjustments on the Boomer, it was found that the umbrella could be installed within a period of 15 h, facilitating faster excavation of the tunnel.

The Pakuashan ridge is an anticlinal structure of rocks, which may be subdivided into two main geological groups. Firstly, 1 m-thick alternations of mudstone or clay of hard to very hard consistency and low degree of cementation, and sandstone, appearing as loose to medium dense sand. Secondly, silty-sandy gravel with cobbles and occasional boulders of maximum diameter 50 cm. The matrix is frequently slightly weathered, and cementation generally poor. Groundwater is a key factor governing rock mass behaviour. Twin tubes with 120 sq m section are being excavated from all four portals, in loose to heavily compacted gravels. The 65 sq m top headings are maintained 60-70 m ahead of the benches, and invert closure follows 6-10 m behind each bench. 20 m-long x 4 in-diameter drainage holes ROCK & SOIL REINFORCEMENT

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are drilled ahead of the face, using casing. Excavation is by backhoe, with a ripper for profiling. Presupport consists of 3 m-long forepoling using SDA around the arch and sidewalls at 0.5 m spacing. Lattice arches are then set at 1 m centres, and 4 m and 6 m SDA cement grouted rockbolts installed, along with two layers of wire mesh and 300 mm of shotcrete. A layer of wire mesh and 200 mm of shotcrete are laid on the floor of the top heading as temporary support. This is the first use of SDA in Taiwan. One in 50 of the installed bolts is subjected to a 17.6 t pullout test. Maximum advance on a top heading has been 3.3 m/day of 24 h, and the site works 7 days/week. Around 800 m from the portals, the faces moved from compacted gravel into sand with very little cohesion, slowing advance rates considerably. Effectiveness of the support regime is measured using arrays of convergence bolts installed at 20 m intervals. There is also a cross section of extensometers at 200 m intervals which measure at depths of 3 m, 6 m, and 9 m into the profile rock. Every 500 m, radial pressure cells and strain gauges are installed in the shotcrete, together with measuring anchors to record stress and strain in the ground. Results from all three sets of stations are analyzed and compared to theoretical behaviour. In addition to the main tunnels, there are nine pedestrian cross passages, three vehicle cross passages, and ten emergency parking bays. A 240 m-deep x 10 m-diameter ventilation shaft has been constructed

Reinforcing Feuerletten Clay In Autumn 1998, work started on a new high speed railway line between the cities of Nuremberg and Ingolstadt, forming the northern part of the proposed high speed connection between the two major Bavarian cities, Munich and Nuremberg. The Göggelsbuch tunnel, which has a total length of 2,287 m and an excavated cross-section of 150 sq m, is the only natural tunnel in the north section of this alignment. It is equipped with an emergency shaft that is connected to the surface by two 150 m-long galleries. Although smaller than the two 7 kmlong tunnelling projects in the middle ROCK & SOIL REINFORCEMENT

Installing 6 m-long SDA at Pakuashan.

in the centre of the alignment using NATM techniques, allowing four more faces to be opened, and facilitating dewatering. A 400 mm-thick cast concrete lining with waterproofing membrane and drainage system will be installed as final support. The mechanical behaviour and engineering characteristics of the gravel formation are related to the degree of cementation of the matrix and the percentage gravel content. Based on the monitoring data, maximum crown settlements of about 400 mm have been observed in areas of fine sediments with ground water, while in sections with dense gravel, 50 mm is typical. Maximum shotcrete stresses of 150-200 kg/sq cm have been measured, within the design shotcrete strength of 210 kg/sq cm.

Project: Nuremberg-Ingolstadt high speed railway. Location: Ingolstadt, Germany. Excavation method: Mechanical excavator. Contractor: Bilfinger Berger and Max Bögl joint venture. Rock: Hard, solid Feuerletten clay. Rock reinforcement requirement: Forward face support, systematic roof support. Rockbolts selected: Atlas Copco MAI SDA, SN anchors. section of the railway, the Göggelsbuch is unique, as its alignment runs through a layer of Feuerletten, a hard, solid clay which is subject to shrinkage cracking when dry. Once in contact with water, Feuerletten softens and becomes impermeable due to a swelling of its clay minerals. 101

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length achieved by coupling sections together, and the quick and economical installation method.

Aerial view of Göggelsbuch tunnel.

Swelling Clay

Supporting the face at Göggelsbuch.

The 35 km-long northern section of the railway line, including the Göggelsbuch tunnel, is under construction by a joint venture of Bilfinger Berger and Max Bögl. It has a reinforced concrete lining varying between 75 and 125 cm in thickness at the invert, and which is a constant 35 cmthick in the arch. A single 3 mm layer of polyethylene membrane helps to seal the tunnel lining against a water head of 30 m. The anchorage systems used in the construction of the tunnel comprised 4 m-long SN anchors and Hollow Bolt Type MAI anchors with varying lengths. Dywidag Systems International (DSI) supplied both systems. The DSI hollow bolt anchor type MAI is optimally used wherever geological conditions would normally require cased drilling to place anchoring or nailing elements. Its advantage lies in the simplicity of the system, the flexibility in its

The Göggelsbuch tunnel runs exclusively in the Feuerletten layer, with between 4 and 20 m of Feuerletten overhead. The clay comprises a clay stone with fine to medium sand, which is locally interrupted by up to 5 m-thick sequences of pure sandstone, and by up to 10 m-thick sequences with alternating sandstone and clay stone. The layers of Feuerletten are usually orientated horizontally. The swelling of the clay, and the pressure exerted, have been examined and analyzed precisely. All the tests demonstrated that the pressure due to swelling, in connection with the hydrostatic load, was not decisive in calculating the internal lining. Groundwater-filled layers of sandstone, and impermeable layers of clay with groundwater flowing on them, were present during the complete advance works. After the whole tunnel had been excavated, an underground water flow of 5 l/s was measured. Construction was from May, 1999 until September, 2000, advancing simultaneously from both north and south portals. The top heading forming the crown was holed through before the bench and invert were started. Concrete lining, from south to north, took some five months from December, 2000 with one wagon for the invert formwork, carrying two forms. Two separately running forms were used for the crown lining, which took another 4-5 months.

Supporting Production The rock was excavated using a tunnel excavator along its entire length, with a hydraulic breaker in sections with thick layers of sandstone. The advance per section was limited to 1.3 m. The tunnel was secured with a 20-35 cm-thick layer of site-mixed shotcrete, and 4 m-long x 25 mm-diameter SN anchors were installed for systematic rockbolting. The crown invert was supported with a temporary shotcrete layer to minimize movement. Trials without the temporary support showed unpredictable results, and the roof above the crown had to be 102

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strengthened over a length of 50 m, due to excessive movement. While advance from the south progressed with hardly any problems, the north drive suffered poor face stability. Despite continuously increasing the density of support, a face collapse occurred in July, 1999. The supports that were installed at that time were: 30 cm of shotcrete in the arch; 20 cm of shotcrete on the arch invert; system anchorage with 4 mlong SN anchors, at 7 units/m; 10 cm of reinforced shotcrete on the working face; 8 m-long MAI R32 face anchors, at 9 units per section; and 6 m-long MAI R32 rods, at 35 units/m. It was decided to keep the same types of support, but those guaranteeing the stability of the working face were intensified. The length of the MAI face anchors was increased to 12 m, and the number doubled to 18 per round. The length of the MAI R32 steel rods was also increased from 6 m to a maximum 8 m. This intensified system of face support was installed over a length of 500 m, once the collapsed face had been cleared. No further collapses occurred on the remaining crown drive, which was completed without further delay.

Self Drilling Anchors at North Downs The Channel Tunnel Rail Link (CTRL) is the link between King’s Cross Station in North London and the tunnel terminal on the coast. This link is being built in two phases. The first comprises the 3.2 kmlong North Downs tunnel along with three other major civil engineering contracts, and was begun in 1998/99. The second phase will comprise four separate contracts and utilize a total of eight TBMs. Phase Two started in 2001. The contract to construct the North Downs tunnel was awarded to Eurolink, a joint venture between Beton und Monierbau of Austria, Miller of the UK and Dumez/GTM of France. The tunnel was constructed through chalk strata common to the region, using NATM techniques. The likelihood of poor ground conditions is increased at the tunnel portal, where the weaker rock has been exposed to weathering. Also, geotechnical engineering calculations show that there are increased ROCK & SOIL REINFORCEMENT

The excavation of the bench and the invert of the tunnel were subsequently completed in about the half the scheduled time, catching up on the contract.

Acknowledgements Thanks are due to Thomas Müller of Bilfinger Berger, and Frank Schmidt of DSI, for describing the construction process.

Excavating the bench at Göggelsbuch.

Project: High speed railway tunnel. Location: North Downs, Kent, England. Excavation method: NATM. Contractor: Eurolink jv of Beton & Monierbau, Miller, and Dumez/GTM. Rock: Chalk with possible flint bands. Rock reinforcement required: Secure portal area for NATM advance. Rockbolt selected: Atlas Copco MAI SDA. stresses where the tunnel barrel is discontinued at the portal. At the London portal, some form of additional ground support was required to allow NATM tunnelling to progress. It was decided to drill a total of 24 holes at 0.5 m centres around the crown of the tunnel. These were installed 15 m deep at 115 mm diameter, using the Atlas Copco Boodex system. The holes were lined with easy-to-handle 1.5 m lengths of attached casing. A false portal was built at the entrance, and the spacing of the steel arches was continued at 1.5 m as the tunnel advanced under the crown umbrella. ■ 103

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Rock Reinforcement at Kemi Chrome Mine Intelligent Mining The large chromite deposit being mined by Outokumpu at Kemi, Finland has a lower than average Cr2O3 content of about 26%, so chromite and ferrochrome production technology has had to be continuously upgraded to remain competitive. The Intelligent Mine Implementation Technology Programme of 14 projects achieved real time control of mine production in precise coordination with the needs of the mineral processing plant and the ferrochrome smelter. The system utilizes a fast, mine-wide information system that can help optimize financial results for the whole operation. Computerized drilling with Atlas Copco Rocket Boomers and Simbas, accurate coring with Craelius rigs, reliable rock reinforcement with Cabletec and Boltec rigs with Swellex bolts and pumps, and the dependability and longevity of Secoroc drilling consumables support this unique mine strategy. The result is cost-efficient, integrated production, on a model which may form the basis of the next generation of mining techniques.

Introduction Outokumpu is one of the world’s largest stainless steel producers, accounting for about 8% of global stainless slab output, and a similar share of cold rolled production. These are hugely significant proportions of a market that has risen by an average of 5.5% per annum over the last 20 years, and is currently enjoying 7% growth. Mainstay of the Outokumpu strategy is its highly cost-efficient fully integrated mine-to-mill production chain in the KemiTornio area of northern Finland. An ongoing investment programme of EUR1.1 billion will expand total slab capacity from 1.75 million t to 2.75 million t, and coil rolling capacity from 1.2 million t to 1.9 million t. 104

Ore reserves at Kemi chrome mine are abundant, and the efficiency of the Tornio smelter is enhanced by its proximity to both the mine and harbour facilities. Mining production has been progressively switched from surface to underground, where intensive use is being made of information technology to optimize the overall mining and processing operation. Underground mining started in 2003 at 150,000 t/y, and production will increase to the planned level of 1.2 million t/y by 2007. Open pit mining will cease in 2006.

Aerial view of Kemi mine, located close to Finland’s border with Sweden.

Reserves The Kemi deposit is hosted by a 2.4 billion year old mafic-ultramafic layered intrusion extending for some 15 km north-east of the

140 m3/s

Kemi underground mine simplified long section.

Backfilling station

70 m3/s 190 m3/s

EAR4

115 Repair shop

FAR2

EAR3

Final pit bottom

Backfill raise

277

Backfill raise

Trial Stoping area 275

300 350 Repair shop

350 Pump station 450 Expl. storage

550 600

450 475 500

500 Pump station and Repair shop

Crusher 580 Pump station

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town itself. The chromite-rich horizon appears 50-200 m above the bottom of the intrusion, and has an average dip of 70 degrees northwest. The main immediate host rock is weak talc-carbonate, in which the hanging wall contact is clearly defined. At the footwall, the chromite and host rock are inter-layered, and must be mined selectively. However, there is strong granite some 80 m below the footwall. The Kemi chrome deposit comprises 11 mineralisations within a 4.5 km-long zone varying from 5-105 m in width, with average thickness of 40 m, a mineral resource of 150 million t of 28.6% Cr2O3. Of this there are 50 million t proven reserves underground between the 500-m level and the bottom of the open pit. The ore body continues at depth, probably to 1,000 m, with 750 m having been reached by the deepest exploratory hole. The 1.5 km-long x 500 m-wide main pit has a final planned depth of 220 m. A two shift/day, five day/week pattern is worked in the mine, from which about 1.2 million t/y of ore grading 24-26% Cr2O3 is processed continuously by the concentrator. The yield is 220,000 t/y of 12-100 mm lumpy concentrate with 35% Cr2O3, and 420,000 t/y metallurgical grade concentrate at 45% Cr2O3. Over the years, some 30 million t of ore have been produced from open pits, resulting in 130 million t in waste heaps.

Ore Grade Control Ore grade control in both the open pit and the underground mine involves intensive wire line diamond core drilling, to determine boundaries and qualities of specific ore types. In addition, all blast holes in the open pit are sampled. Technical innovations for ore characterization and quantification include OMS-logg down hole logging, and automated image analysis for establishing grain size distribution. Basic production data about mineralogical and process histories are logged for each ore stope on a daily basis, and this is merged and compared with daily and blast-specific production histories from the database. Each ore blast is treated selectively at the concentrator, in order to minimize feed variation and maximize process stability. In the concentrator, total chromite recovery is around 80%, depending on the proportion of lumpy ore. Metallurgical grade ROCK & SOIL REINFORCEMENT

concentrate contains about 45% Cr2O3 of 0.2 mm grain size, while upgraded lumpy ore is about 35% Cr2O3 with 12-100 mm size. The former is pelletized at Tornio, and then mixed with upgraded lumpy ore before smelting to produce ferrochrome. Concentrator operation is optimized by accurate calibration of the feed slurry analyzers, and control of product quality from each unit process, both by compensating for changes in feed type, and measuring product quality on-line. Manual input can be used, as well as on-line information. A Craelius Diamec 264 APC drill rig carries out 10 km of coring each year. Drill sections are established every 10 m and downhole survey is standard procedure, using a Maxibore system. Based on the drill hole data, a 3D model of the orebody is created and used as a basis for production planning.

Atlas Copco Rocket Boomer L2 C is used for sublevel development.

Atlas Copco Simba M6 C at work in the sublevels at Kemi mine.

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Atlas Copco Craelius Diamec 264 APC at work underground.

Tying all these streams of collected data and planning outputs together requires an extremely fast communications network, interfacing with a single master database.

Underground Infrastructure

Atlas Copco Boltec LC installing Swellex Mn12 rockbolts.

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The main decline starts at a portal in the footwall side of the pit, at about 100 m below the rim. The decline is mostly 8 m wide x 5.5 m high, to accommodate passing vehicles. It descends at 1:7 to a depth of 600 m at the base of the hoisting shaft, and connects with several intermediate sublevels. The decline is asphalted throughout most of its length. There is also a 5,000 cu m repair shop for open pit equipment at the 115 m level, and a larger 14,000 cu m workshop at the 350 m level for the underground mobile equipment fleet. The final 23,000 cu m main workshop is under construction at the 500-m level. The 350-m level workshops are enclosed by megadoors, which keep in the heat so that an ambient 18 degrees C can be maintained. The service bay is

equipped with a 10 t travelling gantry and 16 m-long inspection pit. The washing bay is equipped with two Wallman hydraulically controlled washing cages, so there is no need for operatives to climb onto the mobile equipment. The main pumping station is located at the 350 m level, and has pumping capacity of 2 x 250 cu m/h. The slurry-type pumps, with mechanical seals, pump the unsettled mine water to the surface with a total head of 360 m. Two other dewatering pumping stations are located at the 500 m and 580 m levels. The crusher station at the 560 m level is equipped with a 1,000 t/h Metso gyratory crusher. This is fed from two sides by vibrating feeders from separate 8 m-diameter main ore passes from the 500 m level, and from one side by a plate feeder, to which the ore can be dumped from the 550 m level. A 40 t travelling gantry crane services the entire crusher house. Crushed ore gravitates onto a conveyor in a tunnel below the crusher for transport to the shaft loading pockets 500 m away.

Underground Production Trial stopes in three areas accessed from the 275 m and 300 m levels were mined to determine the parameters of the bench cutand-fill technique to be used. These had a width of 15 m, and were 30-40 m-long, with 25,000-30,000 t of ore apiece. Both uphole and downhole drilling methods were tested, and 51 mm-diameter downholes selected as being the safest. For production purposes, 25 m-high transverse stopes are laid out, with cable bolt and mesh support to minimize dilution. Primary stopes are 15 m wide, and secondary stopes 20 m wide. Cemented fill, using cement, furnace slag from an iron ore smelter and fly ash from local power stations, is placed in the primary stopes, while the secondary stopes will be backfilled with mine waste rock. The primary stopes are being extracted one or two levels above the secondary stopes. Mining sublevels with 5 m x 5 m cross sections are being established at 25 m vertical intervals, using one Atlas Copco Rocket Boomer L2 C drillrig equipped with 1838 ME rock drills and 5 m-long Secoroc steel and bits. Rounds of 60-80 holes take about 2 hours to drill, charge and prime. An emulsion charging truck with elevating platform and Atlas Copco ROCK & SOIL REINFORCEMENT

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GA15 compressor provides fast and efficient explosives delivery. The footwall granite is very competent, but lots of rock reinforcement is required in the weaker host rock, where all drives are systematically rock bolted and secured with steel fibre reinforced shotcrete. The planned nominal capacity is 2.7 million t/y of ore, which allows for increased ferro-chrome production at Tornio when Outokumpu decides to expand the smelting operation. The total cost for mine development is EUR70 million.

Rock Reinforcement Swellex Mn12 2.4 m-long bolts are used for support in ore contact formations. These are being installed at a rate of 80-120 bolts/shift using an Atlas Copco Boltec LC rig, which is returning drilling penetration rates of 3.2 to 4 m/min. The CAN-bus controlled LC rig mounts the latest Swellex HC1 pump, for bolt inflation at 300 bar pressure, and reports progress on the operator’s screen. The HC1 hydraulic pump is robust, simple, and with low maintenance cost. Coupled to an intelligent system, it reaches the 300 bar pressure level quickly, and maintains it for the minimum time for perfect installation. Combined with the rig’s CAN-bus system, the pump can confirm the number of bolts successfully installed and warn of any problems with inflation. Over 50,000 bolts have been installed to date without problems. A series of slip-pull tests carried out throughout the mine proved the strong anchorage capacity of Swellex Mn12, both in the orebody and for the softer talccarbonate and mylonite zone.

Cable Bolting Kemi installs some 80 km of cable bolt each year using its Atlas Copco Cabletec L unit, which is based on the longhole production drilling rig Simba M7, with an added second boom for grouting and cable insertion. The Rig Control System (RCS), enables the operator to pay full attention to grouting and cable insertion, while drilling of the next hole after collaring is performed automatically, including pulling the rods out of the hole. The main benefit of the two-boom concept is to drastically reduce the entire drilling and bolting cycle time. Also, separating the drilling and bolting functions prevents the ROCK & SOIL REINFORCEMENT

risk of cement entering the rock drill, thereby reducing service and maintenance costs. Kemi tested the prototype Cabletec L and eventually purchased the unit after minor modification proposals. During the testing period, where most holes were in the 6 to 11 m range, the rig grouted and installed cables at rates of more than 40 m/hour. The capacity of the unit, which is governed by the rate of drilling, provided around 50 per cent extra productivity compared with alternative support methods. The Cabletec L is equipped with a COP 1838 ME hydraulic rock drill using reduced impact pressure with the R32 drill string system for 51 mm hole diameter. The machine’s cable cassette has a capacity of 1,700 kg and is easy to refill, thanks to the fold-out cassette arm. It features automatic cement mixing and a silo with a capacity of 1,200 kg of dry cement, which is mixed according to a pre-programmed formula, resulting in unique quality assurance for the grouting process.

Atlas Copco Cabletec L installing cable bolts at Kemi.

Bench Cut and Fill The current mining method is bench cut and fill, a type of sub-level stoping with downhole production drilling, in which primary stopes are 25 m high, 15 m wide and between 30 and 40 m long. Using a Rocket Boomer L2 C rig, the drifts for the primary stopes are developed laterally from the footwall through the ore zone. Then a Simba M6 C production rig drills down 51 mm diameter blastholes in fans 2 m apart. Each stope yields between 25,000 and 35,000 t of ore. 107

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Inside the 350 m level workshop at Kemi.

Tests showed that drilling upwards would be about 30 per cent more efficient, but because of safety issues related to the poor rock conditions, it was decided to start with downhole drilling while getting experience with the rock and the mining method. Meantime, Kemi has ordered a Simba L7 C rig with a long boom to be delivered in August, 2005. With the M6 C and L7 C, operators will be able to cover all kinds of drilling patterns. Mining of the 20 m wide secondary stopes will start in 2005, while sub-level caving with uphole drilling will be tested at one end of the main pit in 2006. Secoroc rock drilling tools are used for production drilling. The previous 64 mm holes over-fragmented the ore, but a switch to 51 mm resulted in lower specific charges and better fragmentation, while retaining the same number of holes. When developing the secondary stopes, the mine may well go back to 64 mm drilling if there are problems keeping the holes open due to the stresses and rock movements. Kemi is carrying out slot hole drilling with a Simba M4 C rig mounted on a Scania truck. The front part of the rig has been redesigned to accommodate the Secoroc COP 84L low volume DTH slothammer, which is used to drill the 305 mm-diameter opening hole for the longhole raises. The blasting holes are drilled off using a COP 54 with 165 mm bit with the same tubes. The 20-m raises are blasted in two 10-m lifts.

Rig Remote Access The drill rigs at Kemi are integrated into the Ethernet WLAN communications net108

work that eventually will cover the whole mine. Currently, this 1 GB network, which is based on commercially available equipment, covers the declines, the workshops and parts of the production area. This network infrastructure not only allows effective underground communication but also means that all the Atlas Copco drill rigs equipped with the Rig Remote Access (RRA) option are logically integrated into the information systems in Outokumpu’s administrative organization. The RRA is installed on the Rocket Boomer and Simba rigs. The RRA, which consists of a communication server on-board the rig and a network adapter, integrates with the mine’s network to allow data transfer and remote monitoring and troubleshooting. It works as a two-way communication system, since data can be sent and received in real-time between Atlas Copco and the mine. For instance, should one of the drillrigs encounter a problem, the warning seen by the operator will also be shown in the mine office, which can then contact Atlas Copco immediately, enabling them to enter the rig’s electronic system and diagnose the fault. The RRA’s main benefits are: the administrative system can be updated automatically with the latest information with no manual handling; the rig operator always has access to the latest production planning; no need to write work reports after each shift, since all log files are automatically saved to the planning department; instead of forcing work orders to be written before each shift, they can be issued during the shift and directed onto the specific drillrig; and fault diagnostics can be conducted remotely, which allows the service technician to diagnose the problem and choose the correct spare parts before travelling to the drillrig.■

Acknowledgements Atlas Copco is grateful to Juha Riikonen, manager of the underground mine for his assistance in arranging the site visit and reading draft. Contributions by Esa Lindeman, open pit manager, Heikki Pekkarinen, concentrator manager, and Jukka Pitkajarvi, chief geologist (all [email protected]). ROCK & SOIL REINFORCEMENT

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Repairing Squeezing Ground at Mitholz Flexibility of Purpose The Satco joint venture, under technical sponsorship of Strabag, installed a complete purpose-designed excavation system at their Mitholz contract on the Lotschberg base tunnel in Switzerland. Speed and efficiency were the key elements of a successful project, for which Satco chose Atlas Copco Rocket Boomer XL3 C drillrigs with ABC Regular semi-automatic boom control for production drilling, and Rocket Boomer L2 C twin-boom machines for the smaller-section work. The rigs were equipped with Secoroc rock drilling tools, and Swellex rockbolts were used for immediate support. This combination of job-matched Atlas Copco equipment, together with first-class on-site maintenance support, helped Satco to get six months ahead of contract schedule over a period of three years. However, close to the boundary of the contracted distance south, the faces unexpectedly hit soft carboniferous banded deposits, some 1,400 m beneath the Lotschen summit. Huge ground pressure was transmitted to the tunnel lining, causing compression and distortion of the steel arches. Satco used its Rocket Boomer XL3 Cs to install 16 m-long MAI SDA self drilling anchors to stabilize the strata for replacement of the steel arches, overcoming a difficult support problem.

Lotschberg Alignment The 34.6 km-long Lotschberg base tunnel, which has been developed from a number of access points, is in an advanced stage of construction, and will be ready for use in 2007. From the base of the 1.5 km-long, 67 sq m Mitholz access adit, located about 8 km from the north portal site at Frutigen, three ROCK & SOIL REINFORCEMENT

main running tunnels are contracted to Satco, a joint venture led by Strabag with Vinci, Skanska, Rothpletz & Lienhard, and Walo Bertschinger. The east and west tubes have been driven by drill/blast some 8.7 km southwards, to meet faces coming north from Ferden. At the same time, the east tube has been advanced some 7.5 km northwards to break out at the Frutigen portal. The west tube from Frutigen portal has also been driven 800 m to junction with the east tube. The nominal cross-section of excavation of the main running tunnel faces is approximately 65 sq m, depending upon the required support, with a maximum of 280 sq m at junction caverns. These have been advanced using sophisticated three-boom and basket Atlas Copco Rocket Boomer XL3 C drillrigs equipped with ABC Regular semi-automatic boom control with two control systems, operated by two drillers working from separate panels. Drillplan data is transferred from the planning office to the machines on PC cards. The big Rocket Boomer XL3 Cs were backed up by a pair of twin-boom Atlas Copco L2 C drillrigs, which handled work

Satco reached Frutigen portal 8 months ahead of schedule.

Wolfgang Lehner, project manager for Satco at Mitholz.

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This arrangement afforded maximum manoeuvring room for the large numbers of mobile equipment in operation. When in good rock, each full, 8 m-wide x 8.5 m-high arched face was drilled out by a Rocket Boomer XL3 C to 4.5 m depth using Secoroc model–37 48 mm, 9-button ballistic bits with R35 thread. Between 105 and 120 holes were normally required, together with two 102 mm breaker holes in the centre. Average drilling rate was 3 m/min, and face and rockbolt drilling took around 3 hours in normal ground. The rock generally comprised good, hard limestone, which could be screened and crushed for aggregate. Total volume of excavated rock was around 1.8 million cu m, of which some 700,000 cu m is being reused.

Excavation and Mucking

Atlas Copco Boomer XL3 C drilling MAI SDA to repair squeezing at Mitholz.

such as bolting, cross passage development, and extraneous excavation. Standard Swellex rockbolts, in 3 m and 4 m lengths, were installed as immediate support, normally at 1.5 m spacing in the roof and shoulders of each drive. All of the ancillary face equipment such as transformers, ventilation extensions, and cable reels were carried on backup platforms suspended on rails slung from the roof. Torqueing up a 16 m-long grouted MAI SDA.

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All blasting at Mitholz utilized site sensitized emulsion (SSE) explosives supplied by Dyno Nobel Sweden. The profile holes were charged at 50% density to control overbreak, and the blasted faces were safened using an excavator-mounted rock scaler. Overexcavation of 45 cm width on horseshoe section and 60 cm width on circular section was required to accommodate squeezing under normal circumstances. An LHD equipped with 5.4 cu m side-tipping bucket carried the spoil back to a 1,000 t/h mobile crusher located some 50-100 m behind each face. From here, the crushed rock was delivered by a 330 m overlap stage conveyor to a 300 t/h trunk conveying system, and thence to a handling plant close to the adit bottom where the rock was further crushed to –200 mm, with oversize scalped by a grizzly. Vertical pocket elevators carried the spoil 20 m up to the adit conveyor loading points, from where two 400 t/h tubed belt systems took it to the surface for transport to the nominated stockpiles. The south section is serviced by two 2,700 kW air conditioning units which are cooled by 150 lit/sec of recycled groundwater, and fresh air is supplied by a pair of 2.4 m ventilation ducts. The air is contained by automatic roller shutter doors, and driven around the faces by auxiliary fans. The Frutigen TBM tunnel is the main fresh air intake and, by the time that the air reaches the south faces, most of it has travelled more than 15 km. All told, there are ROCK & SOIL REINFORCEMENT

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in excess of 120 km of pipelines installed underground for various purposes.

Support and Lining The roof and sides of each excavated round were shotcreted and 20-30 Swellex rockbolts installed, using a Rocket Boomer XL3 C to drill the 38 mm holes. Rock cover varies from 1,000 m to a maximum of 2,000 m beneath the Mitholz peaks. In squeezing ground, wire mesh and steel fibre reinforced shotcrete were used. Rockbursting was a hazard at the far south end of the alignment, especially where crystalline rock was encountered. Permanent lining comprises 250 mmthick cast in-situ concrete formed over a drainage membrane, with the crown of the tunnel positioned 7.2 m above the top of the rail track. The main tunnels are being finished to a standard 62 sq m cross-section. The site worked a 7 day/3 shift operation, with four crews of 9 or 10 men rotating on each face. Tunnelling progress was well ahead of schedule when the south faces reached the predicted water-bearing karstic limestone, the drillrigs having advanced 250-300 m/month on each face, with a maximum achieved of 343 m/month. A complex probe drilling system using 250-300 m-long cored holes was employed to investigate conditions ahead of the face, and average water inflows up to nearly 100 lit/sec were experienced, with a maximum pressure of 54 bar. Hydraulic testing and ground probing radar were also used, and a grouting regime established.

Carboniferous Encounter

profile, they introduced R32 MAI SDA in 8 m and 12 m lengths at a density of ten per metre of advance to replace the grouted rebar. By the end of June, 2004 the ground conditions had deteriorated to the extent that fifteen 8 m-long R32 MAI SDA, eight 12 m-long MAI SDA, and seven 4.5 mlong Swellex were necessary for each metre of advance. Stronger rock reinforcement was required, and it was decided to upgrade from R32 to R38 MAI SDA, in a mix of 8 m and 12 m lengths. This unprecedented density of support sometimes reached 350 m of rockbolting for each metre advance. Nevertheless, squeezing caused deformation over a 100 m-long section close to the face of each drive, causing a pause in advance while the situation was assessed. Each face was secured using 12-15 off 4 m-long fibreglass bolts, and a 470 m-long cored exploratory hole drilled to probe the ground ahead. This indicated that the

MAI SDA under installation alongside replacement steel arch.

Shotcreting a repaired section in the south drives.

In April, 2004, some 1.5 km before the south faces reached the boundary of the Satco contract, a section of softer rock was encountered. This was accompanied by water over a 400 m length, following which the faces progressed through first granite, then limestone, sandstone and shale, before entering an unexpected 600 m-long carboniferous section, in which thin seams of anthracite appeared in the shale. At this point, Satco modified the excavated section from arched profile to circular profile. They had been setting six 6 m-long grouted rebars and four or five 4 m-long Swellex bolts for each metre of advance using the arched profile. For the circular ROCK & SOIL REINFORCEMENT

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circular steel compression arches at 1 m intervals. For each arch, 16 off 16 m-long grouted R38 MAI SDA were installed radially in 4 m-long coupled lengths in 76 mm holes, both to stabilize the strata around the tunnel and to pin the arches in place. These were grouted in place at 2040 bar pressure. Once the relining was completed, tunnelling operations resumed, and were soon into good rock. Satco is carrying on beyond the original contract southern boundary for more than an extra 1 linear km of drive awarded as a bonus for early completion.

North Completion In the north, probeholes were maintained 40 m ahead of the face, drilled in the crown by one of the Rocket Boomer XL3 Cs equipped with a RAS rod adding system. Detection of methane would trigger a warning system on the drillrigs, and the monitoring system on the suspended backup would switch off HT electrics if a dangerous concentration were encountered. Tunnelling at the north face was completed in May 2003, some 8 months ahead of programme, as a result of which Satco was awarded a further contract to excavate some 800 m of the west tube from the Frutigen portal. All cross passage excavation between the east tube and the TBM tunnel is now complete. The main concrete lining operation went well in the north drive, where pair of 12.5 m formworks returned 25 m/day of completed lining. Concrete lining is proceeding apace in the south drives.■

Buckled arch with emergency retaining bolts.

Section of Lotschberg tunnel from Frutigen to Raron. The unexpected area of soft sedimentary rock is delineated by red dotted lines.

2500 2000 1500 1000 500 0

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North Frutigen portal m.s.l. ELSIGHOR ADELRAIN SE-GRAT

Tungsten carbide bit used along with EYY type with MAI SDA at Mitholz.

Acknowledgements

carboniferous section would run out after another 50 m in the west face and 10 m in the east face, following which there would be a transition to comparatively good sandstone. It was decided to reline the deformed tunnel in sections 50 m-long, installing

Atlas Copco is indebted to Satco and Alptransit Lotschberg for permission to publish this article and, in particular, to Wolfgang Lehner of Strabag, project manager at Mitholz, for his assistance with interviews and site visit.

Mithollz lateral adit

Ferden lateral adit LÖTSCHBERG

EGGESCHWAND

Steg lateral adit LÖTSCHENTAL

South Raron portal m.s.l. ST.GERMAN

2500 2000 1500 1000 500 0

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Mechanized Bolting at Zinkgruvan Partners in Production Zinkgruvan Mining AB, Sweden’s third largest mining company, is a part of Lundin Mining Corporation. Zinkgruvan Mining produces zinc and lead concentrates for shipment to smelters in northern Europe. The mine has been continuously in production since 1857, and ore output now stands at about 835,000 t/year, together with 185,000 t of waste from development. Production is obtained from open stopes where, following difficulties with seepage from hydraulic fill when rock quality diminished, the mine now uses paste fill. Rather than deepen the main hoisting shaft, the main ramp access was developed below the 800 m level, and will bottom out at 1,100 m under present plans. Key to Zinkgruvan production efforts is equipment supplied by Atlas Copco, which includes four Simba production drillrigs, three Rocket Boomers and two Boltec rigs, together with maintenance and consumable supply contracts.

Lower Development In order to mine below the 800 m level, the mine uses three Kiruna Electric trucks for ore and waste haulage to the main crusher. A Simba M4 C longhole drilling rig is used on production, drilling up to 40 mlong x 76 mm or 89 mm-diameter blastholes. The machine produces some 50,000 drillmetres/year, while an older Simba 1357 drills a similar number of metres in the 51-64 mm range. The mine is so impressed with the stability of the Simba M4 C rotation unit that it has had an old Simba 1354 rebuilt to incorporate the same unit. A Simba M7 C is being delivered for cable bolt drilling. The drilling consumables are supplied by Atlas Copco Secoroc under contract. The ramp will be driven from the current 980 m to the 1,100 m level. An Atlas Copco Rocket Boomer L2 C is used on ramp and sublevel development, where the requirement is for 18 rounds/week ROCK & SOIL REINFORCEMENT

on a 2 x 7 h shift basis. The mine has an option to purchase a second twin-boom Rocket Boomer, this time an M2 C, which is the mining version of their existing L2 C.

Atlas Copco Rocket Boomer L2 C developing the sublevels.

Rock Reinforcement The mine installs up to 20,000 resin anchored rockbolts each year, and, having upgraded its production process, found that bolting became the new bottleneck. After prolonged testing of the latest Atlas Copco Boltec LC, they ordered two units. Using these machines, the working environment for the bolting operatives has improved immeasurably, since the continuous manual handling of resin cartridges has been eliminated. The Boltec LC is a fully mechanized rockbolting rig with computer-based control system for high productivity and precision. The Zinkgruvan models feature a new type of magazine holding 80 resin cartridges, sufficient for installation of 16 rockbolts before refill. It is equipped with a stinger, which applies constant pressure to keep it stable at the hole during the entire installation process. The operator can select the number of resin cartridges to be shot into the hole, for which the rig air capacity is excellent.

Vital Combination The Rig Control System (RCS) features an interactive operator control panel with 113

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hydraulic system with fewer and shorter hoses for increased availability. Data transfer is by PC-card, which also allows service engineers to store optimal drill settings. The MBU bolting unit on the Boltec LC features a single feed system, utilizing a cradle indexer at the rear end, and a robust drill steel support, plus indexer for grouting, at the top end. It is equipped with a low-mounted magazine for 10 bolts, designed for maximum flexibility during drilling and bolting. The COP 1532 rock drill is the shortest in its class, with modern hydraulic reflex dampening for high-speed drilling and excellent drill steel economy. It has separately variable frequency and impact power, which can be adapted to certain drill steel/rock combinations. The BUT 35HBE heavy-duty bolting boom is perfect for direct, fast and accurate positioning between holes. Large capacity working lights, and a joystickoperated spotlight, ensure that the operator has outstanding visibility from his working position. Atlas Copco Boltec LC installing rockbolts in a development drive.

Grinding Secoroc bits on a Grind Matic BQ2 machine.

full-colour display of the computer-based drilling system. Automatic functions in the drilling process, such as auto-collaring and anti-jamming protection, as well as improved regulation of the rock drill, provide high performance and outstanding drill steel economy. There is integrated diagnostic and fault location, and a distributed

Profitable Collaboration The Rig Control System (RCS), originally developed for Boomer rigs, is now also installed on Simba and Boltec rigs, so the mine benefits from the common concept. Atlas Copco has total responsibility for all service and maintenance operations on its equipment at Zinkgruvan, and has three service engineers stationed permanently at site. The company is also under contract for the supply, maintenance and grinding of Secoroc rock drilling tools, overseen by a Secoroc specialist. From the mine point of view, they believe they have profited by their collaboration with Atlas Copco, particularly in the field testing of the new generation rigs. Early exposure to the capabilities of these machines has allowed them to adapt their mining and rockbolting methods to the new technology, giving them a head start on the savings to be achieved. ■

Acknowledgements This article is based on a paper written by Gunnar Nystrom. The editor also gratefully acknowledges the inputs of Jonas Sodergren, Hans Sjoberg and Conny Ohman, all of Zinkgruvan Mining. 114

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Seismic Tunnelling at Bolu Overcoming Natural Disaster The attempt in the mid-nineties at tunnelling through the Bakacak Fault near the Turkish town of Bolu was aborted following the massive earthquake in November, 1999. This caused the collapse of a section of mined tunnel, which had been excavated with preliminary primary support of soil nails and shotcrete. The overall design has been rethought, and the tunnel is now again under construction. Seismic principles have been applied to this project, which is crucial to completion of the Gumusova-Gerede section of the important North Anatolian Motorway linking Ankara and Istanbul. The design criteria have defined the fault crossing strategy, and the practical solutions involve the extensive use of Atlas Copco MAI Self Drilling Anchors (SDA) as primary support.

History The Bolu Mountain Crossing is midway between Ankara and Istanbul, and represents the most challenging section of the motorway construction. Along this 20 kmlong stretch, four important viaducts and a long tunnel are under construction. The Bolu tunnel is a twin-tube motorway tunnel of about 3 km length, accommodating three lanes per tube, linking the western Asarsuyu valley to the eastern Elmalik village, on the Ankara side. The original design featured five support classes in the tunnel, and two at the portals, with an excavation area ranging between 190 sq m and 260 sq m. The original static design was by Geoconsult GmbH of Saltzburg, Austria, and, for the worst rock condition, involved preliminary excavation and backfill of bench pilot tunnels, a threelayer lining, and a deep monolithic invert. Excavation of the tunnel started in 1993, and, almost immediately, problems were encountered with clays. When the Duzce earthquake occurred in 1999, a stretch of about 350 m of tunnel collapsed behind the eastern faces, and major ROCK & SOIL REINFORCEMENT

damage was done to the lining and invert of both tunnels. Consultants Lombardi SA were brought in to analyze the seismic loads induced by the earthquake, which originated at the North Anatolian Fault. These analyses examined the depth, directional effects, soil amplifications and distance from the seismic source, and a panel of experts was set up to study the results.

Atlas Copco Boomer drilling over the face for forepoling.

Active Faults Two active faults were recognized along the tunnel alignment: the Zekidagi and Bakacak faults (Barka-W Lettis & Associates). The Zekidagi fault dips at almost 90 degrees, is approximately 6 to 8 km-long, and possibly intersects with the tunnel alignment at nearly right angles, around chainage 62+430 in the left tube and

Plan of Astaldi section of the IstanbulAnkara highway.

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Two likely traces of the Bakacak fault, which dips at 40 degrees, were identified crossing the Bolu Tunnel between chainage 62+800 and 62+900 at the left tube, and 52+730 to 52+800 at the right tube, over a distance of about 100 m. This is precisely the zone where excavation was proceeding at the time of the earthquake.

Crossing Active Faults

Standard cross-section of Bolu tunnel showing massive support.

Shotcrete operations underway in the top heading.

52+350 in the right tube, over a length of 25 m to 30 m. It has a potential for small future displacement in the range of 0.150.25 in an earthquake of magnitude 6 to 6.25. This section of tunnel was lined according to the original design, and no particular problems were experienced crossing the fault, although high deformations were recorded. The Bakacak Fault has been identified as a secondary fault in the step-over region between the two major North Anatolian Fault (NAF) branches in the Bolu region. This clay fault exhibits low potential for right lateral strike-slip displacements. It is some 10-45 km-long, composed of several segments ranging from 3 to 5 km-long, and rupture displacements of up to 50 cm can be expected in an earthquake of magnitude 6.25 to 6.5.

Basically, two strategies are feasible to mitigate the seismic risk induced to tunnels by ruptures of active faults across the alignment. These are commonly referred to as over-excavation, and articulated design. In the first case, the tunnel is driven through the fault with an enlarged cross section. A double lining is installed, and filled by a porous material, such as foam concrete. If there is a fault rupture, the clearance profile is guaranteed by the gap between the outer and inner linings. This manner of protection, commonly used for metro projects, is limited by the width of the cross section that must be excavated, and will be most effective when a fault rupture is concentrated within a few metres. The articulated design strategy, on the other hand, reduces the width of the lining segments, leaving independent sections across the fault, and for a distance beside the fault. In a fault rupture, the movement is concentrated at the joints linking the segments, containing any damage in a few elements, without uncontrolled propagation. The maximum length of any single element depends on several factors, such as width of the cross section, expected movement of the fault, compressibility of the surrounding soil, and element kinematics. Articulated design was selected as the most appropriate for the large cross section of the Bolu tunnel, and for the excavation geometry that had already been defined.

Design Philosophy When the Bakacak fault was recognized as active, almost one year after the Duzce event, the restoration of the original tunnel was almost complete, and the shape and type of the cross section adopted was already defined. The bench pilot tunnels of the original excavation had already been backfilled. 116

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The segments geometry was defined by considering a ratio between length and width of the tunnel segment equal to one third, resulting in an element length of about 5 m. This geometry kept the load on the single crown segment below an acceptable threshold value. For practical reasons, the length of the segments was reduced to 4.4 m, with a 50 cm joint gap at invert. This facilitated retention of the original modular reinforcement cage. Following a fault rupture, the tunnel will act longitudinally as an embedded beam, whose extremities are displaced by the lateral offset of the fault. The assumption made, justified by the geologists, is that a rupture will be uniformly distributed across the fault boundaries, with horizontal displacement. Therefore the shear strain in the fault soil can be reasonably assumed as the ratio between expected offset and width of the fault at tunnel level. Up to rupture of the joints, the tunnel will be sheared and bent by the soil as an embedded beam. Once the joint’s shear resistance is attained, each segment will be free to move independently, according to external loads. The maximum acceptable shear resistance of the joint has been defined on an equivalent elastic model, with soil modelled as springs acting in compression. A displacement is gradually applied to the extremities, and the shear stiffness of the joints is designed so as to reach the shear failure of the joint before lateral overload of the element cross section, or bending failure at extremities.

Reinforcement and Joints Across the fault zone, different support measures have been adopted. Of these, the most important is an 80 cm-thick concrete 40 N/sq mm prefabricated concrete slab intermediate lining to be installed between the primary lining and the inner lining. The reinforcement bars have been placed only in the inner (final) lining and at invert, while the shotcrete and intermediate linings have been fibre-reinforced. The primary aim of the reinforcement design is to provide a high ductility to the lining. The allowable rotation has been estimated, and compared to the estimated rotation for the load conditions. This was achieved by introducing stirrups at shear, ROCK & SOIL REINFORCEMENT

keeping the spacing below 30 cm, and also by introducing a light dosage of steel fibres in the concrete mix, or applying an equivalent double mesh layer. These measures were installed within the fault, and up to a distance of 30-40 m from the fault borders. The joints, at 4.2 m spacing, have been detailed to prevent soil squeezing between the segments, and to bridge the static soil pressure to the surrounding elements, but opposing a sufficiently low shear resistance in the event of fault rupture. To provide ring closure of the joint at the invert, a 0.4 m-thick fibre reinforced shotcrete beam is applied to bridge the gap. At the crown, the regular 40 cm-thick shotcrete preliminary lining has been assessed as sufficient. The 50 cm-wide joint is filled by two layers of concrete blocks, with a 10 cm low density PS layer in between. A waterproofing membrane is installed below the concrete block slabs and the invert. In general, at the crown, three levels of linings are installed: a shotcrete lining, an intermediary lining of poured concrete, and a reinforced final lining. The waterproofing membrane bridges the seismic joint gap between intermediary and final lining. The joint opening in the final lining has been enlarged to 70 cm, and the gap will be covered by a steel plate, for the purposes of ventilation and fire resistance. The backfilled bench pilot tunnels were heavily reinforced to provide sufficient abutment to the crown loads during the excavation. These beams cannot be interrupted while excavating, so the cutting of

Installing prefabricated concrete slab intermediate lining.

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General view of the Bolu tunnel face with invert pouring underway.

the joint in the section can only be executed once the invert is in place.

Excavation and Support The Bolu tunnel has been advanced on a new alignment, which diverts around the collapsed section. It is being driven from newly established faces within the abandoned tunnel on the Istanbul side. A 150 m-long cut-and-cover section was completed at the Ankara portals before excavation work could commence from this end. The weathered, faulted amphibolite rock, with up to 140 m cover, is broken up by a Krupp hydraulic hammer mounted on a Cat 235 excavator, then loaded into road tipper trucks. The 7 m-high top heading is opened using 30 x 6 m-long forepoles over the crown, under which three pieces of the Heavy steel reinforcement of the 5 m-deep concrete invert.

5-piece steel arches are set at 1.1 m intervals. Then 20 off, 12 m-long anchors, each comprising 3 x 4 m lengths of Atlas Copco MAI SDA, are drilled in and grouted using an Atlas Copco Boomer drillrig. The roof and sides are given a 40 cm-thick application of steel fibre reinforced shotcrete, and a 50 cm-thick steel bar reinforced shotcrete temporary invert is installed. The bench is then advanced 2.2 m at each side, and the legs of the steel arches are installed, together with bolts and shotcrete. Two incremental advances of 4.4 m allow the invert to be excavated 5 m-deep over the full width of the heading, and this is filled with mass concrete with two prefabricated steel reinforcement cages. A purpose-built, self-propelled stage conveyor is used to transfer the concrete from the fleet of 8 cu m mixer trucks. The invert concreting is maintained within 25 m of the face. The total excavated area of the tunnel is 160-200 sq m. Where the rock is particularly poor, a 60 cm-thick concrete slab intermediate lining is installed, and the annulus backfilled with concrete. This is followed by a mass concrete in-situ lining, using 150 sq m x 13.5 m-long self propelled formworks. The final lining operation is kept within 75-85 m of the face, to ensure permanent support as early as possible. Concrete is supplied from two plants on site with 80 cu m/h output capacity, backed by a 350 t cement storage silo. Where necessary, very-heavy lattice girders are placed as temporary support, and these are cut away as soon as sufficient permanent support is in place. The first tube breakthrough is scheduled for August, 2005, with the second following before the end of the year. The finished twin-tube tunnel will accommodate three lanes of traffic in each direction, with vehicle cross passages at 500 m intervals. ■

Acknowledgements Atlas Copco is grateful to the management of the Bolu project for permission to visit the site, and to Olivio Angelini, Gaetano Germani and Aziz Õzdemir of Astaldi for their help and assistance in preparation of this article. Reference is made to Design and Construction of Large Tunnel Through Active Faults: a Recent Application by M Russo and W Amberg (Lombardi Engineering), and G Germani (Astaldi). 118

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Stabilizing Foundations in Baltic Cities Ancient and Modern The Baltic States of Northern Europe have done well to preserve most of their historic buildings, some dating from the Middle Ages. However, subsidence is now the main enemy in Riga, Latvia and Tartu, Estonia, where the race is on to underpin the buildings most affected. This is being accomplished with minimum intrusion using micropiling techniques, in which MAI SDA and grout pumps are the key elements. Similar techniques are also being used to great effect in Riga coal docks, where the sheet piling of the dock wall is being secured using long grouted SDA while the harbour is deepened. The diversity of these jobs highlights the flexibility of MAI SDA as an essential construction tool.

Riga Coal Dock Riga coal dock handles a million t/y of coal from the Kuzbas region of Russia, and is looking to expand its business by using larger ships, for which the harbour has to be deepened. It was necessary to anchor the existing dock walls to solid ground prior to the dredging operation, following which a new, deeper wall is being installed. Atlas Copco MAI anchors are being used as both temporary and permanent support for the sheet piling operation. Their installation is being carried out by the marine construction division of BMGS, a Latvian specialist contractor. The first stage involved anchoring the upper section of the existing steel sheet piles by drilling from a purpose-built barge floating in the dock, an operation which carried on 24 h/day, 7 days/week whenever the dock was free. The barge had to be towed out of the way every time a coal ship tied up. At each anchor position, a 150 mmdiameter cored hole was drilled 1.5-2.0 m into the dock wall to penetrate the ROCK & SOIL REINFORCEMENT

concrete cladding and the steel sheet pile. Then 47 m-long, 130 mm-diameter holes were drilled 40 degrees below horizontal through the surface sand to penetrate the sandstone bedrock below. Each drillstring comprised a cross bit with 16 x 3 m-long threaded MAI T76 bars and 15 couplings. Continuous grout injection was carried out at 40-60 bar pressure in the 4 h-long drilling operation, during which retarders were used to keep the cement workable. A week later, a plate and nut were screwed onto the protruding end of each anchor, and stressed up to 60 t. Some 120 anchors were required for the first stage, and these were installed in a horizontal line above the high water mark at 3 m intervals. This allowed dredging of the dock from its previous depth of 10 m to 13.5 m. Each anchor was pull tested at 90 t. Sheet piling operations then took place during the winter 2004/2005, along the line of the new dock wall, which is around a metre seawards from the previous position. The annulus between the two walls is being concreted. The second stage of anchoring is being undertaken in 2005, using the same principles as for the first stage. In this case, the

Barge-mounted drillrig installing 48 m-long MAI SDA anchors at Riga docks.

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15 m. The anchors have been designed for a 40-year life expectancy. Inlet grouting

Micropiling For Support Cutter

Anchored rod T76, 3 m - long Sheet pile

Adapter H55-MAI T76

Coupling T76 Concrete

Soil

Pre drilled at ø 150 mm FLOATING PLATFORM

Grouting

The 47 metre-long Atlas Copco MAI Self-Drilling Anchors are drilled through concrete, sheet piles and into the bedrock, strengthening the dock walls prior to deepening the harbour. Drillbit ø 130 mm

Schematic of drillrig mounted on floating platform to drill downward into the harbour wall.

new row of anchors will be drilled between the earlier anchors on the same line, spaced at 3 m apart. This will result in 240 permanent 47 m-long ground anchors at 1.5 m intervals along the dock wall. Dredging work can then be carried out without fear of the dock wall moving, and the dock will be deepened from 13.5 m to MAI 400 grout pump at work in Riga basement.

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The Old City of Riga, much of which was constructed in the Middle Ages, is built upon riverine deposits of the Daugava flood plain, using wooden piles as foundations. When installed in a watersaturated environment, wooden piles will last indefinitely because oxidation is inhibited. For six hundred years, the water table in Riga Old City was stable. Then, in the 1960s, a hydro dam was built across the Daugava River some 20 km upstream of Riga. Since then, the water table has fluctuated, revealing the tops of the wooden piles, and allowing oxidation. The oxidation has promoted rot, and the affected buildings have started to sink. The sinking has not been uniform, resulting in tilting accompanied by severe structural cracking, and differential subsidence along the facades. Halting subsidence of old buildings is not easy, because access is usually difficult, streets are narrow, and working places restricted. This is the precise scenario for which micropiles were developed, and a situation in which MAI anchors and grout pumps prove their value. The theory behind micropiling for support is very simple, seeking to create a higher friction in the existing foundations of the building. This is accomplished by drilling and high pressure grouting through, or in the vicinity, of the base of the structure, to produce crosspiles to support the base of the building. The micropiles are formed by the introduction of grout during the drilling operation. The grout pressure is designed to create piles of the required diameter, while the grout itself stabilizes the hole during the drilling process. Addition of accelerators or retarders allows the installer to vary the set of the grout according to the specific ground conditions, and to ensure that the penetration is sufficient to produce a good pile without wastage. The micropiles are generally drilled tight to the building and as vertical as possible, with a lookout angle of 15 degrees or less. A small crawler rig is generally used, and the grout pump can be remotely ROCK & SOIL REINFORCEMENT

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disposable bit are simply left in the hole, reinforcing the finished pile. Grout is mixed in an MAI M400 pump on which the pressure and quantity can be varied to suit the job. The machine’s galvanized frame and stainless steel charging hopper guarantee corrosion protection and withstand the toughest treatment, and the pump itself is easy to dismantle for cleaning and maintenance. The self drilling aspects of the MAI SDA system allow drilling in unconsolidated or non-cohesive soil which would otherwise require casing, and the hollow rod permits simultaneous drilling and grouting through an adapter, speeding up pile installation. The left-handed standard rope thread accepts standard drill tooling, and can be supplied in a variety of diameters and threads. Generally, if the designer has done his job correctly, and the right diameter of anchor and drillbit are used, the grouting effectiveness can be gauged visually by the appearance of grout at the collar of the hole.

Saving Riga Installing MAI SDA using a handheld pneumatic jackhammer.

situated, possibly conveniently close to the cement storage. The pullout force for a micropile is less than its load bearing capacity, so a hydraulic testing jack can be used to check that any pile has achieved its design capacity, without influencing its function. Overall, micropiling offers a dependable, fast, low-technology, and low intrusion method of underpinning buildings, and the drilling techniques used penetrate both wood and masonry without problems.

FORE, a leading Baltic micropiling contractor, has underpinned a number of ancient buildings and office blocks in Riga Old City. To support the new Hotel Man-Tess, FORE installed 200 micropiles to 8-9 m using MAI R38. The 200 year-old adjacent building was supported by 114 mm steel

Atlas Copco ROC 712HC used by FORE to install MAI SDA.

MAI Self Drilling Anchors The MAI SDA self drilling anchor, although designed primarily to operate in tension, is ideally suited to the requirements of micropiling. For drilling purposes, MAI fully-threaded pipe can be cut into any suitable length, using couplings for extension. This allows the system to be installed in even the tightest situations. Once a hole has reached the required depth, the pipe, couplings and ROCK & SOIL REINFORCEMENT

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L above: Ancient warehouse in Old Riga was saved by underpinning. R above: Subsidence was arrested on the six-storey Pikadilja Cafe.

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pipes installed to 8 m depth at half-metre spacing using an Atlas Copco 712HC drillrig, and filled with concrete. These were then secured using 15 m-long MAI anchors drilled at 7 degrees from horizontal, each providing 30 t of anchoring force. At Pikadilija Café on Valnu Iela, close to the Opera House, the six-storey structure has been subsiding into the very soft deltaic riverine deposit, and needed stabilization before refurbishment. The ground is non-supporting, and the micropiles are designed to take the whole weight of the building at around 20-25 t/unit. Located on the same street as Pikadilija Café, the Terranova building has been underpinned by FORE using 350 micropiles formed from MAI R38 self drilling anchors to 9 m depth grouted using an MAI M400 grout pump at 25 bar pressure. Work was undertaken from both the street and basement of the building to produce crosspile support. In Valnu Street, FORE installed 350 micropiles in the basement of the existing

block, which is being converted to offices and flats. The piles are 15 m deep and 15 degrees from vertical, and designed to pass through the mud layer and penetrate 1 m into the sand layer beneath. MAI R38 SDA grouted by an MAI M400 grout pump produced high friction piles. A 14th Century grain warehouse in Aldaru Iela was underpinned by FORE in 2002 using MAI R38 SDA to produce crosspiles. The subsidence was arrested, and the building, situated close to Parliament House, was refurbished. In a totally different application, FORE is installing MAI R38 8 m-depth grouted anchors to provide stable foundations for new high-voltage electricity pylons crossing Riga docklands.

Preserving Tartu Tartu City Hall has been successfully underpinned using micropiling techniques developed by local contractor Mikrovai, and installed using Atlas Copco MAI SDA self drilling anchors. ROCK & SOIL REINFORCEMENT

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Mikrovai commonly installs 10-12 mlong piles using a 210 mm conical bit and square section pipe, and uses MAI SDA T76 hollow threaded bar for longer micropiles up to 18 m, with bit diameter up to 130 mm. The City Hall was underpinned in 10 weeks using a crew of 8 men. Some 514 holes were drilled and grouted at 20 bar pressure, using a total of 3,100 m of R32 and R38 MAI SDA hollow threaded bar with 76 mm bits. Generally, the R32 micropiles were credited with 15 t bearing weight, and the R38 with 30 t. The subsidence at the City Hall has been successfully arrested, and minor refurbishment works are now being undertaken with confidence. Also in Tartu, an old student dormitory block is being refurbished as a science department for the University. Mikrovai underpinned the basement foundations by installing 230 off 6 m-long R32 micropiles using MAI SDA. These were drilled at 15 degrees from vertical both inside and outside the building. If micropiling were not available as a proven foundation underpinning technique, this building would probably have been knocked down rather than refurbished. At the crossroads in Tartu city centre, a large shopping mall is being constructed by the local Skanska company, for which temporary works include a steel sheet piled retaining wall to the high side of the sloping site. Here Mikrovai has installed 42 off, 14-18 m-long R32 MAI SDA and 20 off, 16-18 m-long R38 MAI SDA to anchor the wall to the sandstone substrata. By drilling at 10 degrees below horizontal, the anchors, spaced horizontally at 4 m intervals along the upper wall section, can penetrate 4 m into the sandstone. The MAI hollow threaded bar has been used in 4 m lengths, with 76 mm EX bits. The R32 anchors have been tested at 20 t and the R38 at 40 t. Because the more traditional wire rope anchors require a casing system of drilling, they take longer to install and are more expensive for this type of job. Once the permanent retaining wall is built, the temporary wall will become redundant and the anchors will be cut ROCK & SOIL REINFORCEMENT

and the sheet piles withdrawn for reuse. Mikrovai has found that the drillbit is critical to a good job, and poor choice can adversely affect the cost equation. A too-small diameter drillbit will result in a smaller grout column than required, and a too-large diameter may cause the hole to collapse. Also, they find that the drilling operation must not be carried out too quickly, because the grout column has to form properly, and this takes a certain time according to the ground characteristics of each job. A rule of thumb when installing 15 m-long anchors is 15-25 holes/day/rig, if access is not a problem. MAI produces a full range of disposable bits in diameters for every condition. ■

Imposing City Hall at Tartu was underpinned in 10 weeks using 3.1 km of MAI SDA.

Acknowledgements Atlas Copco is grateful to Valery Zagulin, chief of BMGS geotechnical department in Riga, Dainis Musins, managing director of FORE, and Urjo Eskel of Mikrovai for their help and assistance in the formulation of this article. Thanks also to Nils Hellgren, managing director of Geomek, representative agent for MAI products in the Baltic States. 123

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MAI SDAs Increase Land Use for English Housing Support for New Housing In the UK soil nailing represents the vast majority of the market for selfdrilling anchors and housing development forms a large part of market growth. At the Admirals Way housing development in the English Midlands town of Daventry, Atlas Copco’s UK MAI distributor, Dywidag Systems International, has been supplying geotechnical specialist contractor Keller Ground Engineering with hollow-bar MAI anchors for clay sub-soil stabilization. Keller also recently carried out similar work at Snodland, Kent to stabilize chalk and clay

Daventry Development The main development contractor at Daventry is a joint venture of Thomas Vale Construction (Site Manager Dave Casey) and Westpoint Construction, tasked with building 26 houses, five pairs of flats and two bungalows on the site. The housing development is on a wedgeshaped, sloping site comprising a relatively soft clay mix which, if developed by conventional means, would probably necessitate the excavation and construction of expensive deep foundations for the houses and service roads. As facilitated by the MAI Anchor soil nailing method, the site has been terraced with embankments supporting the service roads at the end of the gardens of adjacent new properties. The soil nails are installed by drilling into these embankments at 15-20 degrees. A substantial development cost saving will result. At the lower end of the site local conditions over a short length did not permit the creation of an embankment, so here the MAI SDAs were inserted directly into a level surface which would eventually be 124

covered up to form the gardens of some of the new properties. Most UK inland soil nailing applications are classified by geotechnical engineers as low-risk, lightly loaded, passive installations with a design life of 60 or 120 years. Exceptions are coastal areas where the effect of saline water is significant, or in other aggressive ground conditions.

Setting out the embankments in the central part of the housing development. In the background soil nailing is progressing on the section already marked out.

Installing soil nails in one of the development service road embankments.

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MAI SDAs The self-drilling anchors used by Keller at Daventry were of the R32N hollow ropethreaded bar design with 100 mm-diameter, open-face, retroflush sacrificial drill bits suitable for clay. The left-hand thread allows connection to standard drill tooling. The bar, measuring 32 mm diameter over the threads or effectively 29.1 mm has an ultimate strength in this size of bar of 280 kN and yield strength 230 kN. MAI SDAs can be installed in unstable ground without the need for temporary hole casing by simultaneous drilling and grouting. Depending on the type of bit used, they are suitable for a wide range of ground materials including soft clay (as at Daventry), sand, gravel, inconsistent fill, boulders, rubble, and weathered and fractured rock.

inclined 15-20 deg and at right angles to the tracks, permitting the rig to be driven along the row of soil-nails to be installed. The drill bit and rotation speed are chosen to ensure that the borehole is cut rather than

Keller Ground Engineering’s Site Agent, John MacGregor Jr., views the installation of some of the last soil nails to be installed in the lower part of the site.

Installation At Daventry, the consulting engineer’s ground reinforcement pattern called for soil-nail lengths of 5-13m depending on their position on the site. This is achieved by using coupling sleeves to connect the standard lengths of threaded bar. In all 750-760 soil nails are being installed at Admirals Way. A surveyor first lays out each portion of the site to be reinforced using red-painted markers to indicate the planned entry point for each soil nail according to the design of the consulting geotechnical engineer. Keller used two of their own crawlertrack, hydraulic, rotary drilling rigs to install the SDAs, generally with the boom

Reinforcement is complete with a layer of geomat secured by SDA nuts and plates holding fine wire mesh.

Building from foundations commences with the completed embankment reinforcement in the background.

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Installing the top row of soil nails at Woodlands Farm, Snodland, prior to excavating the low part of the slope.

The completed slope stabilization showing the heads of the soil nails and the geogrid later

displacing the soil through percussive action or a high feed pressure. This ensures better permeation of the grout and thus a better bond. Each rod section of the soil nail, three or four metres long, takes only about four minutes to insert using rotary percussive drill action and a 3-man crew. There is a drill-rig operator, another to act as ‘spotter’ and to insert the MAI SDAs and extensions as drilling progresses, and a grout mixer and pump operator. Simultaneous with drilling a cementitious grout is pumped at 2.1-4.1 bar (30-60 lbf/sq.in.) through a special

injection adaptor and thence through the hollow bar of the SDA. The use of large, 100-mm bits enables a sufficiently large grout column to be created to meet the specification. Once the soil-nails are inserted correctly into the ground, sheets of welded heavy wire mesh are attached to the protruding SDAs, followed by a layer of geomat, non-woven, geosynthetic material incorporating a layer of lighter wire mesh. The facing components are held in place by the galvanized plates and threaded nuts of the SDAs. This all acts mainly as erosion control of the stabilized surface, but also aids the stability of the whole installation. Keller’s John MacGregor reported that, on the Admirals Way site, the geotechnical design called for ten ‘test’ soil nails across the site to which tension was applied once the grout had cured. Dywidag’s own Stressing and Testing Services Department carried out all the testing work. A temporary bearing platform is installed since the test load would otherwise be pulling against a soft (clay) face, albeit overlain with geogrid etc. The test establishes the true capacity of the soil nail bond in the stable zone rather than including the effect of the wedge zone.

Prestige Housing Keller Ground Engineering carried out work on another housing development in 2004. The Woodlands Farm luxury housing development at Snodland in Kent, south-east England, represents an important application for embankment soil nailing to make the best use of landscaping. Keller Ground Engineering, working for Berkeley Homes, used 473 R32N MAI SDAs to create an embankment between the building area and a lake in an old chalk pit. The soil nails were 10 or 12 metres total length. Keller employed a drill boom and feed mounted on the long backhoe boom of a hydraulic excavator to install five rows of soil nails in chalk and clay from the top of the embankment. This allowed free access for a bulldozer to shape the bottom of the slope. After installing the soil nails the head plates and nuts were used to retain a geogrid layer of mesh and geosynthetic material to allow restoration with topsoil.■

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Soil Nailing Infrastructure along England’s Routes A Major Force in Transport Slope Stabilization The UK distributor for MAI International, Dywidag-Systems International, has been leading the way in slope stabilization using MAI self-drilling anchors, in conjunction with Atlas Copco Construction & Mining (UK). Some of the most prestigious recent transport construction and renovation projects in the UK have benefited from the use of the MAI SRN hollow-bar anchor system (Self-Drilling Anchors - SDAs), chiefly for soil nailing, whether for stabilization of cuttings walls or embankments.

First Toll Motorway One of the leading projects is the UK’s first toll motorway, the Birmingham Northern Relief Road; now known as the M6 Toll. The engineer working for the Client, Midland Expressway (M6), designed a steep wall in a cutting, protecting some existing trees. The use of slope stabilization with soil nails allowed the ‘footprint’ of the cutting to be reduced (see picture), hence reducing the necessary land ‘take’ from the neighbouring landowner, saving project expenditure. On behalf of the main contractor consortium CAMBBA (made up of Carillion, Alfred McAlpine, Balfour Beatty and Amec), a specialist sub-contractor installed 1000 soil nails using MAI SDAs in a grid pattern across the face of the cutting wall. The ground drilled is sandy clay with occasional boulders, necessitating the use of sacrificial drop-centre button bits with tungsten carbide peripheral blades to form a clean hole. The fully galvanized, R32N hollow-bar, MAI SDAs varied in total length from 7 to 12m with couplers.

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Since this cutting construction was made in February 2003, the M6 Toll now forms a valuable and busy alternative to the previous congested routes of the old M6 and A5 linking the south-west Midlands of England to the North West, by-passing the Birmingham/Black Country conurbation.

Cutting during construction of the M6 Birmingham Northern Relief Road showing the (right) wall stabilized by MAI SDA soil nails compared with (left) a more conventional low-angle cutting slope requiring more surface area and volume of excavation.

Stabilizing Freight Route Britain’s transport infrastructure also includes many kilometres of rail routes, the structures of which often require attention, since many are over a century old. One recent rail project involving MAI SDAs, 678 in all, was the stabilization of a failing embankment on the Crewe-Salop Independent Line in the centre of the Midlands town of Crewe in October 2004. Network Rail (North West) and its Engineer considered the more conventional solution of sheet-piling the lower part of the embankment, but this may have required lengthy closures of a busy rail route, a deeper structure requiring more site investigation, and some other environmental disturbance such as from noise. Using the alternative of soil nailing only limited access from the top of the embankment was required.

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On the Crewe embankment slope installing soil nails with excavatormounted drills. Note protruding heads of installed SDAs

The soil-nail reinforcement was designed in accordance with the new European soilnailing Standard EN 14490, and employed R32N MAI hollow-bar of 16-m length. Only the top-bar (down to the coupler) needed to be galvanized against atmospheric corrosion in order to preserve the structural integrity for the design life of the installation. Two drill booms were used, mounted on hydraulic excavators with long-reach (22m) ‘sticks’. This enabled the soil nails to be installed in the embankment in an ‘underarm’ action, leaving the rail lines below to be operated as normal and without disturbance to neighbouring structures. The drilling equipment included a shank integrated into the injection adaptor enabling simultaneous drilling and grouting.

Badger Bother The restored embankment on the London-Brighton line at Earlswood showing the soil-nailed gabions just below the rail level

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Other Midlands rail projects have been carried out in Railtrack’s (now Network Rail) Midland Zone. Two embankments on the

TSV Line near Henley-in-Arden had been suffering gradual subsidence due to both the type of fill material used and the activities of badgers burrowing in the embankments. The effects of this on the track necessitated the imposition of a 20-mile/h (32-km/h) speed restriction on train movements. Using a series of one-way gates, the badger population was ‘rehoused’ nearby before other rectification work began. Trial soil nails were first tested by Dywidag’s Stressing and Testing Department to establish the bond stress of the nail within the stable zone of the slope, behind the slip plane. Following successful trials a specialist contractor installed the SDAs in both embankments. The method, including simultaneous drilling and grouting, enabled the reinforcement to be installed in the unconsolidated sand and gravel without resort to hole casing, whilst also reducing overall installation time. Following completion of the soil-nail grid, the slope surface was reprofiled, and rail speed restrictions could be lifted. Also in the Midlands, there was a major slip in the Beehive Embankment on the West Coast Main Line in Leicestershire that needed to be rectified in February 2004. The slip had been caused by the presence of a perched water table. The solution involved drainage of the perched water table and the installation of three rows, with 100 soil nails in each, using R32S galvanized MAI SDA hollow bar. The head plates of the SDAs also serve to hold a layer of geosynthetic material in place to deter surface erosion.

Nailed Gabions In March 2003 the Earlswood Embankment, on the main London-to-Brighton railway line, required major stabilization work for the Southern Zone of Network Rail. The Client’s engineers chose a solution combining a layer of gabions immediately under the track with embankment slope soil nailing. Gabions are cuboid steel-wire-mesh baskets filled with rocks to form, with neighbouring units, a self-draining wall. The contractors used MAI SDAs to fix the gabions in position to form a platform under the track, and also inserted the series of soil nails in the underlying embankment. The embankment works were extensive, requiring a total of 1500 soil nails formed by R32N MAI hollow bar. ■ ROCK & SOIL REINFORCEMENT

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Portal Stabilization Using Swellex Olympic Deadline Improvements are being made to the state road EN23 near the town of Porte, Turin in Italy ahead of the 2006 Winter Olympic Games. The project is designed to relieve traffic congestion in the town centre. Tunnel alignment is in gneissgreenstone, mica-schist and glaciallake loose ground, so rock reinforcement is critical to the success of the project, particularly at the portals. Based on its proven quality and consistent performance, Atlas Copco Swellex Mn 16 was selected as the rockbolt for use in stabilizing the rock around the portal.

Mixed Ground The project designer for the underground work is Geodata SpA of Turin, for the client, a consortium known as Agency of XX Winter Olympic Games of Turin 2006. The contractor, Baldassini and Tognozzi SpA Costruzioni Generali of Firenze, Italy, is using drill/blast techniques in the rock sections of the alignment, and a hydraulic hammer in the loose ground. Rock reinforcement is required to improve the quality of the rock, for which Swellex Mn 16 rockbolts in lengths of 4 m and 6 m have been used for supporting the portal area.

in rock comprising gneiss-greenstone and gneiss mica-schist belonging to the metamorphic substratum of the Cristallino Massif of the Dora Maira. Swellex rockbolts were used both underground for primary support, and to reinforce the rock walls above the eastern portals of the tunnels.

Slope Stabilization The geo-structural survey carried out on the slopes housing the portals showed that the

Reinforcement of the slope by the eastern portal of the La Turina tunnel with 4 m-long Swellex Mn 16 rockbolts.

Reinforcement of the slope at the eastern entrance of the Craviale tunnel using 6 m-long Swellex Mn16 rockbolts.

Project Description The project for the diversion of the Colle del Sestriere state road N23 is taking place near the town of Porte, approximately 40 km from Turin, in the upper Chisone Valley of the Piedmont Region. In addition to embankments and dry bridges along the river Chisone, two single-tube, bi-directional natural tunnels are being built, La Turina with a length of 601 m, and Craviale with length of 991 m. La Turina tunnel is being driven partly in rock and partly in softer ground, whereas the Craviale tunnel was driven entirely ROCK & SOIL REINFORCEMENT

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Swellex rockbolts stocked by the eastern entrance of the Craviale tunnel.

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rock was very altered and fractured. These slopes, analyzed using the empirical approach of Romana (1991), were classified as partially stable, and assessed as class IIISMR-Slope Mass Rating. They required immediate support using rockbolts and mesh with shotcrete to avoid the potential slide generated by a combined influence of the joints and inclination of the slope. The formula of Palmstrom (1982) was used to calculate the required number of

bolts based on the number of joints (Jv) per cubic metre of rock. The bolt requirements indicated by this method were: length 3-6 m; distance between bolts 1-3 m; bolt strength 120-150kN; and resulting force applied a 120-150 kN/sq m. To support the walls around the portals, Atlas Copco Swellex Mn16/Mn24 were installed, being the rockbolts with the specified features. Some 450 bolts of 6 m length were used to stabilize the slope at the eastern entrance of the Craviale tunnel, and around 200 bolts of lengths 4 m and 6 m were installed to support the eastern portal of Turina tunnel. Since the sides were reinforced in this fashion, no blocks have moved and the entrances have been stabilized and safely supported.■

References: Palmstron, A., 1982. The volumetric joint count – a useful and simple measure of the degree of rock jointing. Proc. 4th Cong. Int. Assn Engng Geol., Delhi. Romana, M., 1991. SMR classification. Proc. 7th Congr. On rock mech SRM, Aachen, Germany.

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Driving From Budapest to Nürnberg Saving the Best Until Last Completion of missing links in the European Motorway system is rapidly producing fast connections between the most unlikely places. Key elements of the D2/D5 (E65/E50) motorway from Hungary to Germany are the 1.4 km-long twin-tube Sitina tunnel in Bratislava, Slovakia and the 380 m-long Valik tunnel at Plzen in the Czech Republic. These are difficult tunnels, which is perhaps why they have been left until nearly last to be completed. Both are using advanced rock reinforcement techniques to drive through incompetent rock with low overburden. Swellex, Symmetrix, Boodex and MAI SDA are all employed to keep these jobs moving in the right direction, together with Atlas Copco drillrigs and Secoroc drillsteel and bits.

Sitina, Bratislava Contractor Banske Stavby is tunnelling under low overburden in heavy, broken granitoid rock using two Atlas Copco Rocket Boomers equipped with Secoroc T32 Speedrods and 45 – 51 mm bits. Injection grouting is carried out using an MAI m400NT grout pump. The client for the construction is Slovenska sprava ciest, and the designer is Dopravoprojekt a.s, Bratislava. Sitina tunnel comprises east and west tubes, each requiring 251 m of cut and cover at each end and 1,189 m of natural tunnel in between. The natural tunnel is being driven at an excavated section of 7998 sq m in crystalline rock comprising biotite and double-mica granodiorites with sporadic granites, often with veins or pegmatites up to 1.5 m-thick. NATM techniques are used, with five basic rock classes. In classes 1-3, the excavation is divided into a top heading and ROCK & SOIL REINFORCEMENT

bench, and is carried out using drill/blast. In classes 4 and 5 an invert arch is added, and excavation is by mechanical means. Often, a combination of drill/blast and mechanical excavation is employed. Mucking out is by wheel loader into 25 t dumpers. The crystalline rock at Sitina is intensively tectonically disrupted, with systems of 1 mm-3 cm cracks and breaks which

Grouting rockbolts from the basket of the Rocket Boomer 352.

Atlas Copco Rocket Boomer L2 C face drilling at Sitina south.

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radially, using one of the Rocket Boomer drillrigs. The bench is advanced to produce a full excavated section of 105 sq m. The lattice girders comprise three pieces in the top heading, to which legs are bolted as the bench advances. The ground conditions may demand anything from 80 x 1.5 m-deep blastholes using plastic explosives with millisecond delay detonation in the harder sections, to excavator-mounted hydraulic hammer or scaling bucket in the softer sections. There is a serious blasting vibration restriction, due to the proximity of the Slovak Academic Institute with its sensitive technical laboratory equipment. Therefore continuous monitoring is necessary, and parameters are modified to counter undesirable effects. North portals of Sitina with east false tunnel nearing completion.

Symmetrix system umbrella drilling at Sitina portal.

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can be up to several metres wide, and filled with clay material or breccia or mylonite. Locally, coarse blocks of schist-biotite paragneiss of several tens of metres in thickness occur, locked tectonically into the granitodiorites. These discontinuities result in rock splitting to produce large blocks which can fall from the roof and sides of the excavation. The primary lining uses wet shotcrete with a non-alkaline accelerator, lattice girders, mesh and 4-6 m-long grouted rebar rockbolts. The main faces are advanced as top headings, with benches trailing at 50-120 m behind. The 51.7 sq m top heading is micropiled through lattice girders to prevent falling ground, and shotcreted prior to installation of 4 m-long grouted rebar bolts

Symmetrix Complements Boodex Umbrella drilling has been needed throughout the alignment to date, due to the shallow overburden and soft, blocky mylonite. Initially, 12 m-long pipes, comprising 4 x 3 m lengths of perforated Boodex, were drilled in with a pilot bit and disposable crown. These were grouted for 10 minutes at 20 bar pressure to produce a concrete column around each pipe. With 25-33 pipes in each top heading, the grouted columns formed complete umbrellas beneath which it was possible to excavate in 0.8 m increments. Usually eight increments were advanced, and eight arches set and shotcreted, beneath each umbrella, leaving a 5.4 m overlap beneath which the next umbrella could be safely drilled. Lately, Symmetrix has proved cheaper, more reliable, and faster than Boodex where rock conditions have been particularly poor, and some 20 Symmetrix 12 mlong umbrellas have been installed, each comprising 15–20 boreholes. Whereas Boodex employs a pilot bit with a following reamer, which enlarges the hole to allow the casing to be pushed in, the Symmetrix system uses a rotating casing with rock cutting crown behind the pilot bit. Hence Symmetrix provides immediate support for the hole, making it better in very poor ground conditions. Forepoling with up to 40 x 4 m-long, 25 mm-diameter rebar rods is used in the worst ground conditions. In the areas of the main tunnels where the five crosspassages are being excavated ROCK & SOIL REINFORCEMENT

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between the tubes, the invert is concreted to a depth of 1.5 m, and for 10 m on either side. A similar depth of concrete has also been laid at the ends of each of the tubes.

Valik, Plzen Valik tunnel is situated about 30 km from the German border on the Czech Republic section of the Prague-Nürnberg motorway. Overall length of the tunnel is 380 m, comprising 330 m of natural tunnel, with 20 m of cut-and-cover at the west end and 30 m of cut-and-cover at the east end. There is also a 900 m-long surface cutting at the east end to connect with the advancing motorway. The natural tunnel is complicated by shallow cover and a very narrow corridor of surface rights beneath which it has to be excavated. The twin tubes have to be extremely close together, requiring buttress to be excavated and replaced in entirety

Symmetrix or Odex? Both Symmetrix and Odex can be used for drilling holes up to 273 mm diameter, when the choice of bit will depend upon the specific ground conditions, the presence of rock and boulders, and the rig to be used. For shallow holes in soft ground, Odex is cheaper to use, a little slower, will require more torque, and may deviate if hard boulders are encountered. However, a skilled driller will overcome these conditions.

with reinforced concrete before the main tunnel drives could commence. The central pilot tunnel, within which the reinforced concrete buttress for the main tunnel was constructed, was excavated from the west end within a 4.5-month timespan. It was driven as a 4 m-high top heading and 2 m bench, using an Atlas Copco Rocket Boomer L2 C, one of two at site. Main contractor Metrostav also has one Atlas Copco Rocket Boomer 352 at Valik, together with four GIA DC16 service platforms based on Atlas Copco carriers. Excavation was in increments of 0.8 m, 1.0 m, and 1.2 m, depending upon the specific ground conditions, and lattice girders were set at similar intervals. In very soft ground, an excavator with scaling bucket or hydraulic hammer was used instead of the drillrig.

Atlas Copco Rocket Boomer L2 C starting south tube at Valik tunnel.

Valik tunnel west end showing south, pilot and north tube excavations.

Symmetrix is generally used with DTH hammers, but can also be used with top hammers such as the COP 1838 for small diameter holes for applications such as umbrella drilling where the lower torque requirement can be crucial. Both Symmetrix and Odex can be used with all standard casings, and also with HPDE, PVC and fibreglass casings. Drilled casings are becoming increasingly popular in underground construction, especially in urban areas, where they are tending to replace pile driving and pipe jacking in ground containing boulders. In these conditions, Symmetrix is often the only method that can penetrate successfully, and is sometimes called upon to drill down to 100 m.

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holes in the floor of the pilot tunnel, and installed two heavy rebars into each hole before pouring concrete to complete the piles in-situ. The revealed ends of the rebars were hooked, in order to provide a secure connection for the main buttress concrete reinforcement. Likewise, the crown of the pilot drive was reinforced by installation of 4 x 6 mlong grouted rebars per metre of advance to key into the buttress reinforcement. In order to establish the east portals, an 18 m-deep pipe umbrella was installed, together with 6 m-long face anchors. A beam support was also necessary immediately above the east portals, secured by 17 x 20 m-long grouted cable anchors.

Main Tunnels

Buttress formworks inside Valik pilot tunnel.

Immediate support was provided by 4 m-long Atlas Copco Swellex Mn12 rockbolts, with shorter 3 m versions being used in the stronger rock sections. Some 3,000 of the longer units were installed, along with some 2,000 of the 3 m version. Up to 25 Swellex bolts were installed for each metre of advance, with shotcrete being applied systematically to roof and sidewalls, and to the face when necessary.

Concrete Buttress

Section of Valik tunnel showing concrete buttress between main tubes.

The construction of the concrete support buttress between the two tubes of the main tunnel required foundation works through four separate soft ground sections, comprising a total of 90 linear metres. To improve the footing in these areas, 6 mdeep micropiles were installed in rows of four and three at 1 m spacing. This work was undertaken by a specialist subcontractor, who drilled 123 mm vertical

Main tunnel excavations are being undertaken sequentially using NATM techniques. This involves top heading and bench excavation of the outside shoulders of each tube using lattice girders, MAI self drilling anchors SDA R 25 150kN in 3 m and 4 m lengths, and shotcrete. The north tube is being developed in advance of the south tube. Depending on the geology, up to 27 SDA are being installed into each fan or profile, with a 1 m distance between fans. This is followed by two-phase excavation of the upper sections of each tube to form the main tunnel roofs, and then the remaining bench can be removed to construct a curved invert. During the process, the area above the concrete buttress is being grouted for consolidation, to promote transfer of the ground pressure away from the main tunnel lining. The remaining elements of the pilot tunnel lining are being removed on advance. The final lining of the tunnel will comprise reinforced concrete of varying thickness from 0.3 m to 0.5 m. Sitina tunnel is on schedule to open for traffic in August, 2006.■

Acknowledgements Atlas Copco is grateful to Banske Stavby engineers Vladimir Kotrik, Anton Sumerak jr and Anton Petko for permission to extract from their paper Technological Procedure of Construction for the Sitina Tunnel, and to Metrostav engineer Miloslav Zelenka, manager at Valik tunnel, for his assistance at site. 134

ROCK & SOIL REINFORCEMENT

RR3/RC23

24/6/05

13:33

Page 135

OSLO, NORWAY

Systematic Grouting at Oslo Subway Half Century Progress The T-Baneringen project is the biggest enlargement of the Oslo Subway since the system got underway in the 1960s. It comprises several new subprojects, of which the first to be undertaken is the section from Ullevål Stadium to Storo. The alignment of the 1.24 km-long tunnel, with a cross-sectional area of 65 sq m, passes through a very difficult zone between sections 700 and 750, which called for an intense grouting operation. Contractor Veidekke chose the latest grouting technology from Atlas Copco Craelius to handle this challenge, where absolute control over the efficiency of the grouting operation was key to its success. The Unigrout EH 400-100-90 WBC described in this report proved to be the right machine for the job in every respect.

Grouting Contract The contract differentiated between systematic and sporadic grouting, with payment according to work and material quantities. The main components were: drilled metres for investigation; grouting and check holes; quantities of cement; numbers of packers; and the working hours for the grouting operation. The systematic grouting procedure as laid out in the contract included following: 31 holes of 18 m-long; bottom of the hole has to be 5-6 m outside the tunnel contour; and distance between two covers is set at 10 m, or two blasting rounds. In Scandinavian tunneling, leakage figures are most important and are used to

guide the grouting operation. Leakage must be measured and recorded, and leakage per drill hole must not exceed 10 lit/min. The grouting stop pressure is set at 35-45 bar. Leakage