11_Engineering Geology and Soil Mechanics_Chapter 12_Common Usage of Rock and Uncemented Sediment

ENGINEERING GEOLOGY From Palmström A.: RMi – a rock mass characterization system for rock engineering purposes. AND PhD thesis, Oslo University, Norway, 1995, 400 p.

SOIL MECHANICS

CHAPTER 12 岩石

Common Usage of Rock and Uncemented Sediments

未膠結的泥沙

Chapter 2 岩體

৬ᗰ‫ޗ‬ற

ROCK MASSES AS CONSTRUCTION MATERIALS - a rock mass characterization system for rock engineering purposes.

"Rock masses are so variable in nature that the chance for ever finding a common set of parameters and a common set of constitutive equations valid for all rock masses is quite remote." Tor L. Brekke and Terry R. Howard, 1972

A rock mass is a material quite different from other structural materials used in civil engineering. It ฆᔆʳ is heterogeneous and quite often discontinuous, but is one of the materials in the earth's crust, which is most used in man's construction. Ideally, a rock mass is composed of a system of rock blocks and fragments separated by discontinuities forming a material in which all elements behave in mutual dependence as a unit (Matula and Holzer, 1978). The material is characterized by shape and dimensions of rock blocks and fragments, by their mutual arrangement within the rock mass, as well as by joint characteristics such as joint wall conditions and possible filling (see Fig. 2-1). ࡿ‫ف‬ᆏ෻௽ᐛ ᣼ढ ࡿ‫ف‬࿨ዌ

岩體 岩石節理

Fig. 2-1

The main features constituting a rock mass

The complicated structure of the rock mass with its defects and inhomogeneities and the wide range of its applications cause challenges and problems in rock engineering and construction which often involve considerations that are of relatively little or no concern in most other branches of engineering. One of these challenges is, according to Einstein and Baecher (1982), the uncertainties about geological conditions and geotechnical parameters. This is perhaps one of the most distinctive features of engineering geology compared to other engineering fields, therefore 'engineering judgement', adaptable design approaches, and other procedures for dealing with uncertainty or hedging against it have been taken into use. Important in all rock mechanics, rock engineering and design are the quality of the geo-data that form the basis for the calculations and estimates made. This quality depends on two main features. 1. The understanding and interpretation of the geological setting of the area of interest. 2. The way the (known) rock mass at the site is described or measured. The first feature is important mainly in the pre-construction phase and is a result of the geological understanding based on field investigations and the experienced interpretation of available results. To a great extent this is often wholly dependent on the skill of the geologist(s) who decide how the P. 1 of 40

2 - 2 12 CHAPTER

investigations should be done and how the geo-data should be combined. Thus, this process can in many instances be said to be more an "art" than a science. The details concerning the geological part are not dealt with further here, but the influence of the geology is discussed in Chapter 3. The second feature is mainly connected to the present work. Brown (1986) is of the opinion that "inadequacies in site characterization of geo-data probably present the major impediment to the design, construction and operation of excavations in rock. Improvements in site characterization methodology and techniques, and in the interpretation of the data are of primary research requirements, not only for large rock caverns, but for all forms of rock engineering." TABLE 2-1

BASIC ELEMENTS AND RELEVANT CONSIDERED AREAS (based on Natau, 1990)

BASIC ELEMENT

SIZE RANGE

STRUCTURES

CONSIDERED AREA

Crystal lattice

Angstrom size (10-7 mm)

Micro structures

Electron microscope

Mineral grain

Pm - cm

Grain structures in rock

Microscope, hand piece, test sample of rock

Rock material

cm - 10 m

Massive rock

Jointed rock (composed of 'bricks')

cm - 10 m

Joint pattern, rock mass

Geological-tectonical units

10 m - km

Geological-tectonical large size units

Several km

Rock mass volumes between large faults

Hand piece, stone ornaments, building stone, test of rock samples. Foundations, small underground structures, test samples of rock masses, test pits/adits Slopes, tunnels, large underground structures, mines (geological maps and sections) Oil reservoirs, (general geological maps and sections)

Regional plates

INVESTIGATIONS in situ

STRENGTH

in laboratory

SIZE OF SAMPLE Fig. 2-2

The scale factor of rock masses and the variation in strength of the material depending on the size of the 'sample' involved. (After Janelid, 1965)

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CHAPTER 2 - 3 12 Other special features in a rock mass and its utilization in contrast to other construction materials are: the size or volume of the material involved, see Fig. 2-2 and Table 2-1, the structure and composition of the material, the many construction and utilization purposes of it, see Table 2-2, and the difficulties in measuring the quality of the material (see also Appendix 4). TABLE 2-2 MAIN TYPES OF WORKS CONNECTED TO ROCKS AND ROCK MASSES

TYPE

ACTUAL PROCESS OR USE

Treatment of rocks

- drilling (small holes) - boring (TBM boring, shaft reaming) *) - blasting*) - fragmentation*) - crushing - grinding - cutting*)

Application of rocks

ศற - rock aggregate for concrete etc. ഔ‫ ف‬- rock fill ৬ᗰ‫ ޗف‬- building stone

Utilization of rock masses

- in underground excavations (tunnels, caverns, shafts) *) - in surface cuts/slopes/portals *)

Construction works in rock masses

- excavation works - rock support *) - water sealing

*)

Areas where the system is of particular interest.

These factors imply that other methods of data acquisition are used, and that other procedures in the use of these data for construction purposes have been developed. Thus, the material properties of rock masses are not measured but estimated from descriptions and indirect tests. The stress is not applied by the engineering but is already present; the construction, however, leads to stress changes. In the remainder of this chapter the main features of the rock mass and their effect on its behaviour related to rock construction are briefly outlined. 2.1

ROCKS AND THEIR MAIN FEATURES

Geologists use a classification, which reflects the origin, formation and history of a rock rather than its potential mechanical performance. The rock names are defined and used not as a result of the strength properties, but according to the abundance, texture and types of the minerals involved, in addition to mode of formation, degree of metamorphism, etc. According to Franklin (1970) there are over 2000 names available for the igneous rocks that comprise about 25% of the earth's crust, in contrast to the greater abundance of mudrocks (35%) for which only a handful of terms exist; yet the mudrocks show a much wider variation in mechanical behaviour.

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2 - 4 12 CHAPTER

2.1.1 Fresh rocks Each particular rock type is characterized by its minerals, texture fabric, bonding strength and macro and micro structure, see Fig. 2-3. 火成岩

沈積岩

變質岩

Igneous rocks tend to be massive rocks of generally high strength. Their minerals are of a dense interfingering nature resulting in only slight, if any, directional differences in mechanical properties of the rock. These rocks constitute few problems in rock construction when fresh. Sedimentary rocks constitute the greatest variation in strength and behaviour. The minerals of these rocks are usually softer and their assemblage is generally weaker than the igneous rocks. In these rocks the minerals are not interlocking but are cemented together with inter-granular matrix material. Sedimentary rocks usually contain bedding and lamination or other sedimentation structures and, therefore, may exhibit significant anisotropy in physical properties depending upon the degree of their development. Of this group, argillaceous and arenaceous rocks are usually the most strongly anisotropic. Some of the rocks are not stable in the long term, as for example mudrocks, which are susceptible to slaking and swelling. This group of rocks therefore creates many problems and challenges in rock construction. Metamorphic rocks show a great variety in structure and composition and properties. The metamorphism have often resulted in hard minerals and high intact rock strength; however, the preferred orientation of platy (sheet) minerals due to shearing movements results in considerable directional differences in mechanical properties. Particularly the micaceous and chloritic schists are generally the most outstanding with respect to anisotropy. 2.1.2 The influence from some minerals Certain elastic and anisotropic minerals like mica, chlorite, amphiboles, and pyroxenes may highly influence the mechanical properties of the rocks in which they occur (Selmer-Olsen, 1964). Parallel orientation of these minerals is often found in sedimentary and regional metamorphic rocks in which weakness planes may occur along layers of these flaky minerals. Where mica and chlorite occur in continuous layers their effect on rock behaviour is strongly increased. Thus, mica schists and often phyllites have strong anisotropic mechanical properties of great importance in rock construction. Also other sheet minerals like serpentine, talc, and graphite reduce the strength of rocks due to easy sliding along the cleavage surfaces, see Fig. 2-3. Quartz is another important mineral in rock construction. This mineral is grade 7 in the Mohs scale of hardness. Sharp, obtuse-angled edges of the quartz grains have an unfavourable shape regarding drill bit and cutter wear in percussion drilling and TBM boring respectively, while the effect from rounded quartz grains is significantly less. Change of moisture content in swelling minerals of the smectite (montmorillonite) group can cause significant problems related to high swelling pressures (Piteau, 1970). These minerals, occurring either as infilling or alteration products in seams or faults, have in addition to expansion, a low shear strength, which may contribute to rock falls and, in some cases, slides in underground openings and cuttings. Also some rocks may show swelling properties. These rocks can be montmorillonitic shales, altered or weathered basalts, in addition to other igneous, metamorphic rocks, or sedimentary rocks containing anhydrite. P. 4 of 40

CHAPTER 2 - 5 12 Some rocks may slake (hydrate or "swell", oxidize), disintegrate or otherwise weather in response to the change in humidity and temperature consequent on excavation. As mentioned above, an abundant group of rocks, the mudrocks, are particularly susceptible to even moderate weathering (Olivier, 1976). Refer to Fig. 2-3. influence from some minerals

FLAKY MINERALS -mica -chlorite -talc

some special processes acting

SWELLING MINERALS -smectite -montmorillonite -anhydrite

ALTERATION or WEATHERING

HYDRATIZATION of mudrocks etc.

SWELLING ROCKS

ALTERED or WEATHERED ROCKS

SLAKING ROCKS

common rock features

MINERAL COMPOSITION MINERAL SIZE TEXTURE fresh rocks

Fig. 2-3

HOMOGENEOUS and LAYERED ROCKS

SCHISTOSE ROCK

rocks with isotropic or slightly anisotropic properties

rocks with strongly anisotropic properties

r o c k s w i t h r e d u c e d s t r e n g t h a n d d ur a b i li t y

The main variables influencing rock properties and behaviour

2.1.3 The effect of alteration and weathering The processes of alteration and weathering with deterioration of the rock material have reducing effect on the strength and deformation properties of rocks, and may completely change the mechanical properties and behaviour of rocks (refer to Fig. 2-3). For most rocks, except for the weaker types, these processes are likely to have great influence on engineering behaviour of rock masses. Hence, the description and characterization of rock masses should pay particular attention to such features. Rocks are frequently weathered near the surface, and are sometimes altered by hydrothermal processes. Both processes generally first affect the walls of the discontinuities 1. The main results of rock weathering and alteration are: 1. Mechanical disintegration or breakdown, by which the rock loses its coherence, but has little effect upon the change in the composition of the rock material. The results of this process are: - The opening up of joints. - The formation of new joints by rock fracture, the opening up of grain boundaries. - The fracture or cleavage of individual mineral grains. 1

In this work, the following terms have been applied for the various types of discontinuities: Joints - Minor and medium sized discontinuities, including fissures, cracks, fractures, breaks, etc.; also some minor seams are included in this group. Seams - Filled discontinuities, including shears; they are also named 'singularities'. Weakness zones - Including faults, crushed zones and zones of weak rocks surrounded by stronger rocks. The characteristics of these features are further described in Appendices 1 and 2.

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2 - 6 12 CHAPTER

Chemical decomposition, which involves rock decay accompanied by marked changes in chemical and mineralogical composition results in: - Discoloration of the rock. - Decomposition of complex silicate minerals (feldspar, amphibole, pyroxene, etc) eventually producing clay minerals; some minerals, notably quartz, resist this action and may 'survive' unchanged. - Leaching or solution of calcite, anhydrite and salt minerals.

2.

The disintegration leads mainly to a greater number of joints in rock masses located in the upper zone of weathering, while decomposition influences the joint condition as well as the rock material. 2.1.4 Geological names and mechanical properties of rocks Rocks that differ in mineral composition, porosity, cementation, consolidation, texture and structural anisotropy can be expected to have different strength and deformation properties. Geological nomenclature of rocks emphasizes mainly solid constituents, whereas from the engineer's point of view, pores, defects and anisotropy are of greater mechanical significance (Franklin, 1970). For each type of rocks the mechanical properties vary within the same rock name. Petrological data can, however, make an important contribution towards the prediction of mechanical performance, provided that one looks beyond the rock names to the observations on which they are based. It is, therefore, important to retain the names for the different rock types, for these in themselves give relative indications of their inherent properties (Piteau, 1970). 2.2

DISCONTINUITIES IN ROCK ࡿ‫ف‬ऱլຑᥛࢤ

Any structural or geological feature that changes or alters the homogeneity of a rock mass can be considered as a discontinuity. Discontinuities constitute a tremendous range, from structures which are sometimes thousands of meters in extent down to - per definition - mm size, see Fig. 2-4. ROCK DEFECTS

JOINTS

WEAKNESS ZONES

faults

ឰᐋ

褶皺,折疊 joints partings cracks fissures bedding planes seams / shears 0.01

0.1

1

10

100

1000

10 000

LENGTH (m) Fig. 2-4

The main types of discontinuities according to size. The size range (length) used for joints in this work is indicated.

The different types, such as faults, dykes, bedding planes, tension cracks, etc. have completely different engineering significance (Piteau, 1970). The roughness, nature of their contacts, degree and nature of weathering, type and amount of gouge and susceptibility to ground water flow will vary greatly from one type of discontinuity to another since their cause, age and history of development are fundamentally different. The effect on rock masses due to these localised discontinuities ࡿ‫ف‬ऱլຑᥛࢤ

P. 6 of 40

CHAPTER 2 - 7 12 varies considerably over any given region depending on structure, composition and type of discontinuity. The great influence of discontinuities upon rock mass behaviour calls for special attention to these features when characterizing rock masses for practical applications. Joints and faults have numerous variations in the earth's crust, this is probably the main reason that it has been so difficult to carry out common observation and description methods (Terzaghi, 1946). 2.2.1 Faults ឰᐋ Faults are breaks along which there has been displacement of the sides relative to one another parallel to the break. Minor faults range in thickness from decimetre to meter; major faults from several meters to, occasionally, hundreds of meters. It is important to realise that most fault zones are the result of numerous ruptures throughout geological time, and that they quite often are associated with other parallel discontinuities that decrease in frequency and size in the direction away from the central zone. Faults and fault zones often form characteristic patterns in the earth's crust consisting of several independent sets or systems, see Fig. 2-5. The main directions, which mainly were determined by the state of stress, have often the same orientations as the joint sets within the same structural area.

0

Fig. 2-5

1km

Weakness zone

Lake

Pattern of weakness zones and faults in the earth's surface. (After Selmer-Olsen, 1988)

Hydrothermal activity and other processes may have caused alteration of minerals into clays, often with swelling properties. Many faults and weakness zones thus contain materials quite different

P. 7 of 40

2 - 8 12 CHAPTER

from the 'host' rock. The problems related to weakness zones may, therefore, depend on several factors which may all interplay in the final behaviour. Weakness zones and faults show numerous variations in their structures and compositions, see Fig. 2-6. In cases where the zones or faults are composed mainly of joints and seams they may be characterized by the same descriptions as for jointing. In other cases it may be necessary to characterize them by special descriptions and measurements or tests, as further described in Appendix 2. The fact that faults and weakness zones of significant size can have a major impact upon the stability as well as on the excavation process of an underground opening necessitates that special attention, follow-up and investigations often are necessary to predict and avoid such events.

D

E

A Fig. 2-6

B

C

Sketches of some types of weakness zones. A - C are from ISRM (1978) and D - E from Selmer-Olsen (1950).

褶皺,折疊

2.2.2 Joints and their main features Joints are the most commonly developed of all structures in the earth's crust, since they are found in all competent rocks exposed at the surface. Yet, despite the fact that they are so common and have been studied widely, they are perhaps the most difficult of all structures to analyse. The analytical difficulty is caused by the number of fundamental characteristics of these structures. There is, however, abundant field evidence that demonstrates that joints may develop at practically all ages in the history of rocks (Price, 1981). A joint can be open or closed. Closed joints may be nearly invisible. Yet they constitute surfaces along which there is no resistance against separation. In quarries the spacing of joints determines the largest size of blocks of sound rock which can be obtained. Therefore, joints and joint systems have attracted the attention of builders ever since cut stones have been used. A joint is composed of several characteristics. In addition to length and continuity of the joint the main are: - roughness and strength of the joint wall surface, - waviness or planarity of joint wall, - alteration or coating of the joint wall, and - possible filling. Refer to Fig. 2-7. P. 8 of 40

CHAPTER 2 - 9 12

All these parameters influence on the shear strength of the joint (Brekke and Howard, 1972; Price, 1981; Hoek and Brown, 1980; Barton et al., 1974; Barton and Choubey, 1977; Bieniawski, 1984; Turk and Dearman 1985; and several other authors). They also determine the amount of water that can flow through the joint. ity ontinu and c length

joint of the

int of jo it ion ce: d n o fa c sur wall thness ting

a oo - sm ssible coalte ration - po ssible k o p ro ll c of wa

joint thickness and possible filling material waviness or undulation of joint wall

Fig. 2-7

Sketch showing the main features of a joint.

The distance between the two matching joint walls controls the extent to which these can interlock. In the absence of interlocking, the properties of the filling of the joint determine the shear strength of the joint. As separation decreases, the asperities of the rock wall gradually become more interlocked, and the rock wall properties are the main contributor to the shear strength. 2.2.3 The main jointing characteristics By jointing is meant the pattern and frequency or density of joints. Field studies of several workers have shown that the joints preferentially are found in certain directions. One to three prominent sets and one or more minor sets may occur; in addition several individual or random joints are often present. The joints delineate blocks. Their dimensions and shapes are determined by the joint spacings, by the number of joint sets and by random joints. ISRM (1978), Barton (1990) and several other authors state that the block size is as an extremely important parameter in rock mass behaviour. A number of scale effects in rock engineering can be explained by this feature including compressive strength, deformation modulus, shear strength, etc. Different methods are used for measuring the jointing density. The most common are: Joint spacing, either in surfaces or in drill cores or scan lines. Density of joints, either in surfaces, or in bore holes or scan lines. Block size, in surfaces, and Rock quality designation (RQD), in drill cores. They are further outlined in Appendix 3, where also correlation equations between them have been developed.

P. 9 of 40

2 - 10 12 CHAPTER 2.2.4 The rock mass Discontinuities ranging in lengths from less than a decimetre to several kilometres divide the bedrocks into units, volumes or blocks of different scales (Fig. 2-8): 1. The regional pattern or first order fault blocks are bounded by the larger weakness zones or faults (see Fig. 2-5). 2. The second order blocks formed by singularities, i.e. small weakness zones or seams. 3. The third order blocks formed by normal joints. 4. The small joints in the appearance of bedding or schistosity partings form the smallest pattern or fragments, which are of interest for engineering purposes. 5. The microcracks are responsible for making up small fragments or grains in the rock. These discontinuities are, however, mostly considered a rock property and are therefore generally included in the strength characterization of the rock material. Based on this it has been found useful for engineering geological and design purposes to divide the ground into: - "The detailed jointing" formed mainly by the third and fourth order blocks or units, and - "The coarse pattern of weakness zones" formed by the first order blocks or units by faults and weakness zones.

A

2

3

1

2

4 3

B

3 A

4

2

50 -

2

500

3

- 15

00 m

2

15 0m

5

4

B

5

5-

Fig. 2-8

50 m

Simplified model of various dimensions units or blocks formed by discontinuities of different size (after Pusch and Morfeldt, 1993).

P. 10 of 40

2 - 11 12 CHAPTER

This corresponds with the division suggested by Selmer-Olsen (1964). The rock blocks in the detailed jointing pattern including the rock fragments or pieces caused by the small joints/fissures is a main feature in the rock mass characterization developed herein. 2.3

ROCK MASS CHARACTERIZATION FOR DESIGN AND CONSTRUCTION PURPOSES

An important issue in rock mass description and characterization is to select parameters of greatest significance for the actual type of design or construction. There is no single parameter or index, which can fully designate the properties of jointed rock mass. Various parameters have different significance and only if combined can they describe a rock mass satisfactorily (Bieniawski, 1984). Testing of rock masses in situ has brought out very clearly the enormous variations that exist in the mechanical behaviour of a rock mass from place to place. According to Lama and Vutukuri (1978) the engineering properties of a rock mass depend far more on the system of geological discontinuities within the rock mass than of the strength of the rock itself. Further, the strength of a rock mass is often governed by the interlocking bonds of the unit "elements" forming the rock mass. Terzaghi (1946) also concludes that, from an engineering point of view, a knowledge of the type and frequency of the rock discontinuities may be much more important than of the types of rock which will be encountered. Similarly, Piteau (1970) has stressed the importance of distinguishing between the behaviour of the rock and the rock mass, especially for hard rocks. Thus, characterizing a discontinuity system in a way that describes the variability of its geometric parameters constitutes an essential step in dealing with stability problems in discontinuous rock masses (Tsoutrelis et al., 1990). This does not mean that the properties of the intact rock material should be disregarded in the characterization. After all, if discontinuities are widely spaced, or if the intact rock is weak, the properties of the intact rock may strongly influence the gross behaviour of the rock mass. The rock material is also important if the joints are discontinuous. In addition, the rock description will inform the reader about the geology and the type of material at the site. Although rock properties in many cases are overruled by discontinuities, it should be brought to mind that the properties of the rocks highly determine the formation and development of discontinuities. Therefore, an adequate and reliable estimation of the nature of the rock is often a primary requirement. For some engineering or rock mechanics purposes the mechanical characterization of rock material alone can be used, namely for drillability, crushability, aggregates for concrete, asphalt etc. Also, in assessment for the use of fullface boring machines (TBM), rock properties like compressive strength, hardness, anisotropy are among the more important parameters. Kirkaldie (1988) mentions a total of 28 parameters present in rock masses which may influence the strength, deformability, permeability or stability behaviour of rock masses: 10 rock material properties, 10 properties of discontinuities and 8 hydrogeological properties. Because it is often difficult or impossible in a general characterization to include the many variables in such a complex natural material, it is necessary to develop suitable systems or models in which the complicated reality of the rock mass can be simplified by selecting only a certain number of representative parameters. For this purpose several classification and design systems have been developed, of which some are shown in Table 2-3 for information. Further, Table 2-4 indicates the main rock mass and ground features and which of these that have been applied and combined in the various systems. P. 11 of 40

2 - 12 12 CHAPTER

From Table 2-4 it is seen that the following parameters are most frequently applied in design and classification systems: the rock material (rock type, geological name, weathering and alteration, strength); the degree of jointing (joint spacing, block size, RQD); and in situ stresses. Also such features as: orientation of main discontinuities or joint set; joint conditions; block shape or jointing pattern; faults and weakness zones; and excavation features (dimension, orientation, etc.) have been considered as important parameters in rock masses. TABLE 2-3 SOME OF THE MAIN DESIGN AND CLASSIFICATION SYSTEMS IN USE Name of classification

Form and Type*)

Main applications

Reference

The Terzaghi rock load classification system

Descriptive and behaviouristic form Functional type

For design of steel support in tunnels

Terzaghi, 1946

Lauffer's stand-up time classification

Descriptive form General type

For input in tunnelling design

Lauffer, 1958

The new Austrian tunnelling method (NATM)

Descriptive and behaviouristic form Tunnelling concept

For excavation and design in incompetent (overstressed) ground

Rabcewicz, Müller and Pacher, 1958 - 64

Rock classification for rock mechanical purposes

Descriptive form General type

For input in rock mechanics

Patching and Coates, 1968

The unified classification of soils and rocks

Descriptive form General type

Based on particles and blocks for communication

Deere et al., 1969

The rock quality designation (RQD)

Numerical form General type

Based on core logging; used in other classification systems

Deere et al., 1967

The size-strength classification

Numerical form Functional type

Based on rock strength and block diameter; used mainly in mining

Franklin, 1975

The rock structure rating (RSR) classification

Numerical form Functional type

For design of (steel) support in tunnels

Wickham et al., 1972

The rock mass rating (RMR) classification

Numerical form Functional type

For use in tunnel, mine and foundation design

Bieniawski, 1973

The NGI Q classification system

Numerical form Functional type

For design of support in underground excavations

Barton et al., 1974

The typological classification

Descriptive form General type

For use in communication

Matula and Holzer, 1978

The unified rock classification system

Descriptive form General type

For use in communication

Williamson, 1980

Basic geotechnical classification (BGD)

Descriptive form General type

For general use

International Society for Rock Mechanics (ISRM), 1981

*)

Definition of the following expressions: Descriptive form: the input to the system is mainly based on descriptions Numerical form: the input parameters are given numerical ratings according to their character Behaviouristic form: the input is based on the behaviour of the rock mass in a tunnel General type: the system is worked out to serve as a general characterization Functional type: the system is structured for a special application (for example for rock support)

P. 12 of 40

CHAPTER 2 - 13 12 As for most other construction materials, there is also in rock engineering and construction a need for a strength specification of the material, i.e. the rock mass. The strength of other construction materials can be determined from the process of refining or ensured during production of the material. In rock construction, however, the material already exists, the task is to evaluate the strength properties it possesses (and not to produce them). The considerations outlined above have been important in the development of the present system for rock mass characterization. TABLE 2-4 APPLICATION OF ROCK MASS AND GROUND PARAMETERS IN VARIOUS DESIGN AND CLASSIFICATION SYSTEMS CLASSIFICATION SYSTEM NO. Æ ROCK - Origin, name, or type - Weathering - Anisotropy ROCK PROPERTIES - Unit weight - Porosity - Rock hardness - Strength - Deformability - Swelling

1

2

3

JOINTING GEOMETRY OR STRUCTURE - Joint orientation with respect to excavation - Jointing pattern - Continuity - Structure (fold, fault) EXTERNAL FEATURES - Water conditions - Rock stress conditions - Blasting damage - Excavation dimensions

5

6

7

8

9

10

x

x o

"

:

11

12

x +

x

13 x

+ +

x

+ +

x

x

o

x :

:

o

: : :

JOINT CONDITIONS - Joint size/length - Joint separation - Joint wall smoothness - Joint waviness - Joint filling DEGREE OF JOINTING - Block size - Joint spacing/frequency - RQD - Number of joint sets

4

x

x o

x

o

o

x x

:

:

o

x x x

: x

x

x o

x

x x

x

x

x

x

x x

+ x

: :

: :

o

:

o

o + x

:

x x

x + + x

x x x

CLASSIFICATION SYSTEM NO. Æ 1 2 3 4 5 6 7 8 9 10 11 12 13 Legend: x well defined input o very roughly defined or included : included, but not defined " partly included (in other parameters) + used as additional information (in RMR as adjusted value) Classification system no.: 1 Terzaghi (1946) 5 Deere et al. (1969) 8 Wickham et al. (1972) 11 Matual and Holzer (1978) 2 Lauffer (1958) 6 RQD (1966) 9 RMR (1973) 12 Williamson (1980) 3 NATM (1957-64) 7 Franklin (1970, 1975) 10 Q-system (1974) 13 BGD (1981) 4 Coates and Patching (1968)

Go to Page 31 Uses

of Soil (Uncemented sediment) P. 13 of 40

CHAPTER 12 Supplementary Notes of Rock Masses as Construction Materials

構造地質學 I

褶皺,折疊

斷層

地殼的

背斜層 翼

P. 14 of 40

CHAPTER 12

向斜層

山脊

山槽

two 軸平面

P. 15 of 40

CHAPTER 12 波長

等傾斜的摺叠

P. 16 of 40

CHAPTER 12

傾斜

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CHAPTER 12

P. 18 of 40

CHAPTER 12

熔岩層 石灰岩

塑性流動

P. 19 of 40

CHAPTER 12

傾角

擦痕面

劃痕

擦痕

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CHAPTER 12

P. 21 of 40

CHAPTER 12

Օ୹ߣʳ

聖安德烈亞斯

P. 22 of 40

CHAPTER 12

Օ୹ߣʳ

P. 23 of 40

CHAPTER 12

地壘

斷層崖

地溝;地塹

萊茵河谷

P. 24 of 40

CHAPTER 12

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CHAPTER 12

六角岩石節理

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CHAPTER 12

日光

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CHAPTER 12

傾倒破壞 節理 (裂縫)

P. 28 of 40

CHAPTER 12

Weathering of Granite in Hong Kong

花崗岩的風化

球狀風化

球狀風化 花崗岩的風化

碳酸鹽

高嶺土

P. 29 of 40

Chapter 12 14 Structural Geology I CHAPTER Self-assessment Exercises 褶皺

1. 2. 3. 4. 5.

6. 7. 8.

Describe how folds are formed. With the aid of a labeled diagram, show the characteristics of folds. Describe how faults are formed. 斷層 With the aid of labeled diagrams, distinguish between a normal fault and a reversed fault. Describe the following terms: — Syncline and anticline 向斜層;背斜層 — Punch or pitch 傾斜 — Dome and basin — Horst and graben 地壘;地溝,地塹 — Symmetrical fold and unsymmetrical fold — Step faulting What are the differences between faults and joints? What are the effects of folding on rocks? What are the effects of joints on rocks?

Back to Page 6 DISCONTINUITIES IN ROCK

P. 30 of 40

ENGINEERING GEOLOGY AND SOIL MECHANICS

CHAPTER 12 Common Usage of Rock and Uncemented Sediments Uses of Soil (Uncemented sediment) Soil or uncemented sediment plays a significant part of the construction industry. It is used as a foundation for homes and buildings. Soil compaction is used to increase the density of the soil and ensure its stability. Compacting the soil also prevents soil settlement and reduces water seepage. The strength of soil is measured before a construction project to determine how easily the soil changes shape and whether it is capable of maintaining under the weight of a building. Working on the wrong type of soil may lead to cracks in the foundation, leaks and floods. Just like other construction materials soils has its own scientific analysis with regards to its abilities on dealing with forces. Being the oldest construction and probably engineering material soil is one of the most complex fields in civil engineering to the point that when it comes to the factor of safety in design whatever has direct contact with soils, e.g. foundations, or soil based constructions, e.g. embankments, requires a significantly higher safety factor compare with other construction materials, i.e. the uncertainty in soil analysis and design is higher. This is most likely resulted from the way soil originates. Usage of soil as the main element of construction goes back to the first civilization when Sumerian built Ur, first city in the history, on south of Mesopotamia near the mouth of Euphrates River. They used bricks to build their first houses and earlier they built embankments and dams to direct the water for irrigation. The Western history of recognition the soil as a main element goes back to Romans, in the first century B.C., when their engineers used the trial and error experiences to construct foundations. After all today soil and rock are still one of the most important materials used in construction. It is used or on its natural state or with improvements, such as compaction, reinforcement and etc., as the main component such as in dams, embankments and highways or as supporter element in every construction, i.e. foundation support. Soil material is also a critical component in the mining and construction industries. Soil serves as a foundation for most construction projects. The movement of massive volumes of soil can be involved in surface mining, road building and dam construction as well as reclamation. Soil material is extensively used in earthfilling works or the use of natural or screened soils as road construction materials as well as in projects involving slopes, tunnels, foundations, etc).

P. 31 of 40

CHAPTER 12 1.

Earthwork

Filling materials must be available and compaction must be properly performed to prevent settlement. Earthworks fill material may consist of soil, rock, or inert construction and demolition material. Fill material shall be capable of being compacted to form stable areas of fill. Earthwork fill materials when deposited are normally loose and bulked. It is therefore necessary to compact the materials so as to prevent softening, dislodgment and settlement of the earth. Fill material shall be compacted in layers to a stable condition. The thickness of each layer shall be 150 mm to 300 mm which depends of the capacity of the compaction plant used. The amount of compaction attained is measured by “dry density” of the fill. Generally, the fill material shall be compacted to obtain a relative compaction of at least 95% of the “maximum dry density” of that material. 2. Founding materials for footings and foundations Should possess adequate Bearing capacity 3. Reclamation With proper fill treatment

P. 32 of 40

Reclamation is the process of depositing materials either in the sea or in 鬆軟的 low-lying swampy areas in such a way that useful areas of land are CHAPTER 12 formed. Almost any type of material can be used for reclamation, 填海工程 depending on the use to which the land is to be put. This will range from 3. Reclamation agricultural land and land for light industrial uses, which can utilise 承載力 materials which have low load-bearing capacities, to land for the 3.1 Purpose of Reclamation construction of dock and harbour installations and power stations, which will require high quality incompressible materials.

Reclamation may generally be carried out: 基礎建設

z

To provide land for essential major transport infrastructure. 公眾休憩用地

z

To provide land for housing, community facilities and public open spaces.

z

To provide land for port and industrial uses. 水力情況

z

To eliminate areas of badly polluted water and improve hydraulic conditions by 海岸線

The main phases of reclamation are:

堆料 rearranging the coastline. 1. Site establishment and mobilisation; 2. Dredging of a stockpile;

3. Construction of sea walls or bunds; 4. Pumping sand behind sea 堤 walls or bunds; and 5. Stabilisation of surface.

填海方法

3.2 Reclamation Method

Factors affecting the operation of reclamation areʳLocation of site, ʳ Type of material and Transport of materials

排水方法

3.2.1

Drained Method U

海洋沉積土

The drained method leaves the soft marine deposit in place, and the consolidation is U

U

排水豎管

加載預壓法

usually accelerated by the use of vertical drains and sometimes with surcharge preloading.

Drained reclamation is usually carried out in the following sequence:

填海土 排水砂層

土工織物；隔泥紡織物料 海積淤泥

排水帶

沖積土

排水砂層；疏水層 排水豎管

Sequence of Drained Reclamation U

3.2.2 Fully dredged method 3.2.3 Partial dredged method

P. P. 33 12 of of 40 30

CHAPTER 12

土工織物；隔 泥紡織物料

a.

Laying of geotextile on the seabed U

U

Geotextile may be laid on the seabed to separate the fill from the underlying soft marine deposits, preventing migration of fines. It also enhances the stability of the underlying marine deposits in supporting the loading of the reclamation fill. b.

Deposition of blanket layer U

排水砂層；疏水層

This blanket should consist of free draining granular material of about 2 m thick. This granular layer works with the vertical drains to enable drainage from the clayey deposits. It also acts as a capping layer to spread the load from the fill during the filling operation. 排水板；排水 帶；排水心管

排水豎管

c.

排水肩帶；排水 板；排水帶

Installation of vertical drains (also known as wick drain or band drain) U

U

無紡

The vertical drain was band-shaped with a plastic core enclosed by a non-woven geotextile filter jacket. It functioned as a passage for water flow, to accelerate 消散

the dissipation of pore water pressure during the consolidation of the marine deposit layer.

The band drains were installed in a triangular grid pattern with

1.5 m c/c spacing.

By Land Plant

By Marine Plant

Installation of vertical drains U

To commence the acceleration of consolidation earlier, the band drains are usually installed over water using special marine plant just after laying of the sand blanket.

The vertical drains can also be installed after reclamation using

land plant. P. 13 34 of 40 P. of 30

CHAPTER 12

Wick Drain

Installation of Wick Drain 排水板；排水 U

U

帶；排水心管

d.

淺築,放置

Controlled thin-layer placement U

Controlled even placement of thin layers of fill on the reclamation site is necessary to avoid shear failure of the underlying marine deposits and the 泥波

formation of mud waves.

An initial thickness of no more than one meter of fill

is usually required with subsequent layers increased as appropriate. 躉船

液壓堆填

夾泥

Placement

車尾傾卸填土法

can be by bottom-dump barges, hydraulic filling, grabbing or end tipping.

End Tipping 車尾傾卸填土法

Hydraulic Filling U

液壓堆填

Grabbing 夾泥

Bottom-dump Barge 開底運泥船

P. P. 14 35 of 30 40

CHAPTER 12 Fully Dredged Method 全面挖泥方法

3.2.2 U

沖積黏土

沖積粉土

In fully dredged method, all marine and alluvial clays or silts are removed by U

U

dredging and replaced with fill. Pros: U

x

The method is relatively simple.

x

Settlement of the reclamation fill is more quickly and more predictable.

Cons: U

x

Can be expensive where thick layers of soft deposits exist.

x

Causing mud waves during dredging

x

Disposal of dredged sediments, particularly for contaminated mud may be problematic.

This method is generally discouraged unless there is strong justification.

3.2.3 x

Partial Dredged Method U

局部全面挖泥方法 沖積土層；沖積物

The partial dredged method involves partial removal of marine or alluvial U

U

deposits, leaving the lower, stiffer or stronger deposits in place. x

The remaining marine deposits shall be treated as that in the drained method. 排水方法

x

It fact it is the combination of the drained method and fully dredged method, so it combines and neutralizes both the pros and cons of the two methods.

P. P. 36 15 of of 40 30

CHAPTER 12 3.3 Fill Materials

填料 碎石

Fill materials for reclamation includes public fill, marine sand fill and crushed rock, but public fill and marine sand fill are the most commonly used types of fill in local conditions. 3.3.1 x

Public Fill U

公眾填料 拆建物料；建築和拆卸物料

惰性部分

Public fill is the inert portion of construction and demolition material from private and public developments and demolition sites.

x

拆卸地盤

Because of the shortage of areas to accommodate the public fill generated by the construction industry, priority should be given to its use.

x

It is also the government policy to maximize the use of public fill in reclamation projects.

海沙填料

3.3.2 x

Marine Sand Fill U

挖泥船

Sophisticate dredgers are use to obtain the sand from a marine Suction hopper dredger 吸式開底挖泥船

borrow area. x

動員成本

Since the mobilization costs are high, the size of the project must be large enough to justify the use of sophisticated dredgers.

x

爬吸式開底挖泥船

Plant such as trailing suction hopper dredgers may dredge marine sand fill very 採泥區

fast and at relatively low costs, particularly when the borrow area is close to the reclaimed site. x

填海地盤

These dredgers can deposit marine sand in the reclamation by bottom dumping or by hydraulic pumping.

x

The rate of formation of reclamation can be very rapid compared to the use of other types of fill. P. P. 37 16 of of 40 30

CHAPTER 12 3.3.3 x

Rock Fill U

碎石；填石

碎石

Crushed rock from local land sources should not normally be used for reclamation. It should be used as foundation materials or processed to produce 骨料；集料；碎石產品

aggregate products, as far as possible. x

In case a works project involving large quantities of rock excavation and removal, the surplus rock material can be used for reclamation.

x

Where crushed rock over 250 mm is used, it should be placed in areas where no 妨礙,阻礙

building development will take place, to avoid impeding piling or excavation works in the future.

3.4 Fill Treatment x

填土處理

Fill treatment processes are to speed up the consolidation of the reclaimed area in order to reduce the long term settlement.

x

It shall be noted that the settlement is contributed from both the existing marine deposits and the newly reclaimed materials.

3.4.1 x

Surcharge Preloading U

預加荷載

Surcharge preloading can be used to accelerate settlement of fill that would otherwise occur more slowly.

x

Monitoring of the consolidation of the fill will be carried out periodically.

x

The surcharge should only be removed when the required settlement or increase in strength has been achieved. Drainage Layer

Vertical Drain

Vertical Drains 排水豎管

Surcharge Pre-loading P. P. 38 17 of of 40 30 U

預加荷載

CHAPTER 12 3.4.2 x

Dynamic Compaction U

動力壓實；動力夯實

Dynamic compaction involves repeated dropping of heavy weights onto the ground surface.

x

Large amounts of energy are transferred to the soil in the form of impact force and waves, particularly shear waves.

x

This results in a densely packed particle arrangement.

x

動力壓實

Dynamic compaction is suitable for use in most soils except cohesive soil below the water table.

x

磅砲

The pounders used for dynamic compaction may be concrete blocks, steel plates, or thick 鋼制砲彈

steel shells filled with concrete or sand, and may range from one or two up to 200 tons in weight. Drop heights up to 40 m have been used. x

Dynamic compaction can also be carried out

Free Fall Hammer 自由落下錘 U

水底

underwater.

彈坑,陷口 Craters Formed by

Free Fall Hammer U

Free Fall Hammer

U

自由落下鐵鎚

P. 39 40 P. 18 of of 30

CHAPTER 12 3.4.3 x

Vibro-compaction U

震動壓實

The vibro-compaction method is used to compact a thick layer of fill, particular in reclamation.

顆粒狀的泥土

x

It is used for granular soils, in particular sand.

x

This method is very similar to the stone column method except that no additional granular material will be used to fill the borehole; instead the original fill material is pushed back into the borehole.

x

振浮壓實器

The vibroflot is penetrated into the fill and retracted in a controlled motion such that a dense column of fill is formed.

x

The compaction is carried out in a triangular grid pattern of 2.5 m to 4 m c/c spacing.

x

Effective compaction depth can be up to 35 m.

x

Vibro-compaction is only applicable to granular materials of certain grading

顆粒材枓

properties. x

Vibro-compaction cannot effectively compact the surface few metres of fill and therefore separate compaction of the surface layer will be required.

Vibro-compaction Method 震動壓實 P. 40 19 of of 40 30 P.