ADVANCED GEOTECHNICAL SOLUTIONS FOR MODERN HIGH SPEED RAILWAY LINE

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Symposium International GEORAIL 2011 International Symposium

ADVANCED GEOTECHNICAL SOLUTIONS FOR MODERN HIGH SPEED RAILWAY LINES SOLUTIONS GEOTECHNIQUES AVANCÉES POUR LES LIGNES DE CHEMIN DE FER MODERNES À GRANDE VITESSE Gerhard SCHULZ ARCADIS Nederland, Amersfoort (The Netherlands) ABSTRACT - A railway line, especially a high speed railway line, requires high safety, high availability and low maintenance. Therefore it is essential to overcome the separation of substructure and superstructure as well as of different structures along the line (like tunnels, bridges, culverts, embankments and cuts). Interfaces have to be bridged. Since earth structures are the main part of the railway net, the quality of the earth structures are mainly decisive for the success or the failure of a high speed line. Geotechnical engineering plays an important role. Some measures for earth structures are presented in order to reduce maintenance and life cycle costs. RÉSUMÉ – Une ligne de chemin de fer, tout particulièrement une ligne à grande vitesse, doit offrir une sécurité élevée, une grande disponibilité et de faibles besoins d’entretien. Il est donc essentiel de traiter convenablement la séparation des superstructures et de leur support ainsi que la succession d’ouvrages différents sur une ligne (comme des tunnels, des ponts, des buses, des remblais et des déblais). Des ponts doivent être établis sur ces interfaces. Comme les ouvrages en terre constituent l’essentiel du réseau ferré, la qualité de ces ouvrages est décisive pour le succès ou l’échec d’une voie à grande vitesse. La géotechnique joue un rôle important. Quelques dispositions pour les ouvrages en terre sont présentées, avec pour but de réduire les coûts d’entretien et de cycle de vie. 1. Introduction Without doubt concrete structures like bridges, culverts and tunnels will be planned in detail, while for earth structures the final design often mainly comprises just the angle of the slope and the gradient and dimensions of the drainage. But bridges and tunnels are only a minor part of the whole railway net. In Germany, for example, bridges and tunnels account for about 3% of the whole railway net (mainly conventional net), while 97% of the track are on earth structures. For some high speed lines the percentage of earth structures might be less (about 40 to 70%) due to the different allowed alignment parameters of the track. But still earth structures are the main body even of a high speed line. The percentage depends mainly on the topography and on the character of rail traffic (only passenger traffic or mixed traffic for passengers and freight). For WuGuang Railway PDL in China, currently with about 1000km of length the longest and with an operation speed of 350km/h also the fastest high speed railway line in the world in operation, the percentage of earth structures is about 43% (tunnels: 18% and bridges: 39%). This line is dedicated only to passenger traffic. 143

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These numbers show the significance of earth structures in the railway net. To increase the competitive capacity of railways the operation costs of the net have to be lowered and the availability of the infrastructures adjusted to the needs of the customers has to be guaranteed. Availability means among others, that the operation speed is adjusted to the needs. Sections with reduced speed due to defects are not acceptable. A financial optimum between maintenance and investment has to be found. The significance of earth structures in this context can already be seen from its percentages in the railway net mentioned above. Earth structures must “survive” the life cycle of a line, while the concrete structures have already been replaced or at least renovated. The great importance of earth structures controverts the fact, how they have been disregarded during design and construction in the past. This all causes that earth structures usually contain the highest risk regarding costs; costs of construction and costs of operation as well. Or shortly: the earth structures are decisive for the success or the failure of a high speed line. Besides the safety, the serviceability (and therefore the deformations) plays a major role and has to be evaluated. Usually the settlements will be calculated in cross sections. But decisive are especially differential settlements. Therefore a longitudinal evaluation of the settlements is required. Earth structures have to be designed and constructed as carefully as it is usually done for tunnels or bridges. Essential is a smooth track without discontinuities. A continuous track has to be constructed and not just a chain of single structures. 2. Some principles about earth structures Vertical deformations (settlements) are added by the following components (Figure 1): ƒ Settlements of the subsoil. ƒ Settlements of the embankment itself. ƒ Settlements due to traffic (dynamic impact).

Figure. 1: Settlement Components Apart from the total value of the settlements the development of the settlements with the time is essential. The different components occur at different times, but are also superposed. Settlements of the subsoil can be calculated according to the well-known geotechnical principles. These settlements decrease with the time depending on the permeability of the subsoil (=consolidation). Countermeasures to reduce and/or accelerate these settlements can be taken. Countermeasures can be: pre-loading, surcharge/overloading, soil replacement, 144

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subsoil improvements etc. For high and very high embankments there is no effect of surcharge/overloading, because the additional load applicable is very low compared to the total load of the high or very high embankment. So in the case of high and very high embankments this method cannot be applied to accelerate the settlements. The settlements due to traffic (dynamic impact) mainly depend on the stiffness of the upper layers under the rails. Therefore higher requirements are defined for the upper layers under the rail (about 2.5m below the ballast bed) on embankments but also in cuts. The dynamic stability of the subsoil has to be guaranteed. By compliance with these requirements the settlements due to traffic (dynamic impact) will be in the range of some millimetres. The settlements of the embankment itself summarize all the vertical deformations between the top and the bottom of an embankment during the life cycle.. Due to the different influence factors these settlements cannot be calculated, they can only be estimated based on previous experience. In literature values of 0.2% to 3% of the height of the embankment are indicated. That means for an embankment of 20m height settlements between 4cm and 60cm. These settlements can continue over years (“creeping”) and can differ in short distance. These settlements are mainly responsible for the “bumps” on some highways. These settlements depend on the filling material used, the quality of the compaction, the porosity of the filling material, the atmospheric conditions, the alteration of the filling material, etc. As it can be seen from the example (Laechler, 1998) also horizontal deformations can occur in the same range as the vertical deformations (= settlements). These deformations can be minimized by detailed planning including the choice of the filling material and good, void free and homogenous compaction of the filling material. 3. Earth structures and track maintenance It is essential for a successful high speed railway line to lower the maintenance efforts. Therefore it is necessary to overcome the separation of substructure and superstructure as well as of different structures along the line (like tunnels, bridges, embankments and cuts). That means maintenance including repair works can be minimized by an optimized substructure (, which respects already the requirements of the superstructure and the operational requirements) and by constructing a continous track and not just a chain of single structures. In principal there are 2 approaches for high speed lines: 1. optimizing track maintenance 2. avoiding track maintenance as much as possible Both approaches imply regular inspection (assessment of present condition), service (service works like lubrication and grinding of the rails to maintain the status) and repair (reestablishment of defined status), whereupon the 2nd approach intends to avoid as much as possible the cost- and time- intensive repair works. Therefore the 2nd approach led in the last consequence to the application of slab (or ballastless) track instead of ballasted track. The 1st approach follows more or less the old practice used in conventional railways with ballasted track and regular repair works including tamping, lifting and grinding operations. Carrying out these works requires a regular time frame of several hours without operating trains, usually during nighttime, which also requires only passenger trains and no mixed traffic of passenger and freight trains. 145

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Since (due to the deterioration of the ballast) regular tamping as a measure of geometrical corrections is required anyway as part of maintenance while applying conventional ballasted track, the need of limiting residual settlements and especially differential residual settlements hasn’t been respected so much in the past by applying ballasted track. But experiences have shown, that maintenance works in track sections on embankments are higher compared to other sections and that the maintenance works increase with the height of the embankments (Lopez-Pita, 2006). These increased maintenance and repair works could significantly be reduced by optimizing the construction of embankments and limiting the residual settlements and differential settlements. Records about maintenance including repair works of railway authorities in different countries can hardly be found in the engineering literature. For the evaluation, the experiences after the first 10 years of operation (from 1992 to 2002) of the high speed line from Madrid to Seville in Spain with ballasted track (published by Lopez-Pita, 2006) should serve: - acceleration exceedance levels are especially high in the section of switches and expansion joints; - track sections on embankments have a higher deterioration. Maintenance works increase with the height of the embankment. Significant effects on maintenance works can be observed in track sections on embankment higher than 10m high as opposed to embankments of less than 5m high; - track sections on bridges present almost twice the deterioration rate than in normal plain track. This is mainly due to the higher stiffness of the structure, which leads to higher wear of the ballast; - track sections in the transition area between earth structure and bridge have a higher deterioration rate. This shows the negative impact of different vertical stiffnesses along a track; - track sections over small rigid structures (like culverts) have a very high deterioration rate. This shows also the negative impact of different vertical stiffnesses along a track; - track sections in tunnels have a much lower deterioration rate; - the use of softer railpads can considerably reduce track maintenance needs. 4. Solutions Some authors focus on the elasticity of the rail pads, This shall not be the subject of this paper. The focus of this paper shall be the optimization of the substructure. According to the experiences with maintenance of high speed railway lines mentioned above it is worth to concentrate on the construction of embankments, the area of culverts and the transition from embankments to bridges. 4.1 Construction of embankments For environmental and economical reasons the materials excavated in cuts and tunnels have to be used as much as possible for embankment fillings. Transportations should be reduced, in order to save resources and minimize environmental impact. The experiences with embankment dams can only partly be transferred to embankments for high speed railways. For embankment dams mainly the stability is important, that means high shear strength (high friction angle) and the permeability of the filling material. 146

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Settlements and deformations in general are secondary for embankment dams, but are essential for embankments for high speed railways. Originally the regulations to the design and construction of earthworks for railways were based on techniques for highway works, but have been developed and specified further according to the special requirements of high speed railways. It has to be considered, that the dynamic impact of high speed traffic is higher than the one on highways. Different settlements on embankments for highways can easier be rectified than on embankments for high speed railway lines. Due to the high speed the typical “bumps” known from highways and roads are unacceptable for high speed lines because of safety risks. For high speed railway lines, sections with reduced speed and/or closing of even only one track for repair works are expensive and are constraining the operation significantly. Therefore besides the stability also requirements regarding the serviceability have to be fulfilled. Most national standards allow the use a rock fill materials, while the maximum grain size is limited - usually to 2/3 of the thickness of the compaction layer. Often the material as excavated will be used for compaction while casually crushing in-situ during compaction and separating the bigger boulders. A void less structure can hardly be achieved with such a material (Entenmann, 2001). For the long term stability, hard unweathered rock material, which is resistant to water and the atmospheric conditions expected and will therefore not alter, is required. But such material is often not available and/or could be used for other purposes (e.g. base and drainage layers, ballast or aggregate for concrete). Weathered and soft rocks like e.g. claystone, siltstone and most sandstones don’t fulfill the requirement of long-term stability. For the quality control of the compaction of such materials the commonly used direct methods (e.g. Proctor tests) are not applicable. Therefore it is not astonishing, that several publications (Laechler, 1998; Cuellar, 1999; Veiga Pinto, 1999) report long-term deformations and inhomogeneities of rock-fill embankments, even though complete monitoring of deformations of embankments can hardly be found. In the low mountain ranges in Germany hard unweathered rock can only be found in great depth, that means during tunnel excavation in tunnels with high overburden. But due to the process of tunnel construction, this material accrues erratically and in batches less than the capacity of embankment construction. That’s why for several high speed lines in Germany during the last 10 to 15 years obviously less qualified material like silt, sandy clay, soft and weathered clay-, silt and sandstone has been used while stabilizing these materials with binder (cement and mixtures of lime and cement). These materials are usually available in the cuts adjacent to the embankments in sufficient batches and will therefore not disturb the construction process of the embankments. These materials will be stabilized with binder (mixed-in-place). In order to guarantee a homogenous mixed material, to save binding material, to enable the mixing on the site with a rotary hoe and to get a homogenous filling the maximum grain size should be limited to 20mm. This can be achieved by using a packer unit, if necessary. Afterwards the material will be compacted in layers of 30cm with pad foot roller (Figure 2). Required compaction degree: 97% (simple Proctor test) and porosity less than 12%. This method can also be understood as the consistent application of the technical backfill normally used in the transition area to bridges.

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Figure 2: Emplacement of soft rock stabilized with cement Since the first consequent application at the high speed line from Cologne to Frankfurt (started operation in 2002), it has also been applied on most of the other high speed lines in Germany (e.g. high speed line from Nuremberg to Ingolstadt (started operation in 2006), high speed line from Ebensfeld to Erfurt and Leipzig/Halle (currently under construction). It will also be applied on the project Stuttgart21 including the high speed line from Stuttgart/Wendlingen to Ulm, which just started construction. Due to the significant advantages it is more and more also applied for highway constructions. There are a lot of positive experiences (also long-term experiences) with this method now. It has now also encroaches on technical specifications and standards as so called “qualified soil improvement (qualifizierte Bodenverbesserung)”; (BetonMarketing, 2007; Ehrlinger, 2006; Kuhl, 2005; Nijland; Schulz, 2004; Kliesch, 2002; Kocan, 2005). In principal this method is not new. In the past adding lime to filling materials has been used in order to reduce the water content and enable the compaction of this filling or adding cement has been used to make a material resistant to frost and to increase the bearing capacity. New is the purpose of the stabilization proposed: namely to produce a material with the physical properties needed for a high speed line with high availability and low maintenance efforts. The physical properties needed can be adjusted by the content of binder and the kind of binder used. In most of the cases a content of binder of 2 to 4% has been sufficient.

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The advantages of this method (Duerrwang, 1999; Schulz, 2004) are: - a homogenous and void free embankment filling is produced; - a high and homogenous deformation modulus of the embankment filling is achieved; - differential stiffness along the track are minimized; - long-term stability (no swelling, no softening) is achieved; - the stiffness of the embankment bridges weaknesses in the underground. Therefore different settlements will be equalized; - deformations of the embankment itself are reduced to zero (also in long term); - the material is dynamically stable; - the material is less sensitive to water. So construction and compaction is nearly independent from the weather (except during frost); - construction risks are minimized; - the stabilized material has a high cohesion. So, even though the friction angle is less than for rock fill material, the stability can be guaranteed and is even higher than for rock fill; - “spreading” of the embankment cannot occur; - nearly every material is suitable, as long as the particle size can be handled by the rotary cutter. 4.2 Embankments in combination with pile-like elements Due to the stiffness of the material the embankment loads can be transferred to piles, limecement columns or other elements needed to decrease the settlements of the subsoil. Usually the content of binder is increased to about 4 to 7% (depending on the material and the properties required) in the lowest layers for this application. Compared to geogrids often used to transfer the embankment loads and to carry horizontal loads and/or tensile stresses, the solution with stabilized filling materials can reduce horizontal deformations significantly (Figure 3).

Figure 3. Reducing horizontal deformations by applying stabilized filling material

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4.3 Area of culverts Traffic routes are often crossed by different kind of culverts. Each culvert represents a discontinuity, which causes very high deterioration rates of the track (Lopez-Pita, 2006). Due to its stiffness the stabilized embankment can bridge such discontinuities and equalize the settlements (Figure 4). Also the vertical stiffness are harmonized.

a. Calculations

b. Measurements Figure 4: Settlement curve in an area of a typical culvert 4.3. Transition from embankment to bridge Critical due to different settlements and stiffness are always the transitions from embankment to bridge (Lopez-Pita, 2006). Most national standards recommend a technical backfill with a wedge of cement-stabilized gravel. The above mentioned method can just be applied also in the transition from embankment to bridge. By raising the content of binder the stiffness can be successively increased. Usually the intention of the engineer for the bridge is to found the abutments and the piers as stiff as possible and to avoid settlements. Therefore most of the bridges on compressive soils are found on piles in the subjacent rock or incompressible soil. But this foundation causes a “settlement leap” from the embankment to the bridge (Figure 5: Left side). 150

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To avoid this leap and to harmonize the settlements of the embankment and of the bridge the Piled-Raft-Foundation can be applied. With the Piled-Raft-Foundation only a part of the load is carried by the piles and the remaining load is carried by the raft. The piles are used as “brake” of the settlements. The Piled-Raft-Foundation is a well known method for the foundation of high rise buildings (El-Mossallamy, 1996; Stahlmann, 2001). In combination with the above mentioned stabilization of the filling material of the embankment it can significantly equalize the settlements at the transition from embankment to bridge (Figure 5/Right side) and can also be an economical solution.

Figure 5: Foundation of the abutment of bridges Left side: Conventional (= Piled) Foundation / Right side: Piled-Raft-Foundation Anyway a joint evaluation of the settlements of the embankment and of the bridge in longitudinal direction of the line (and not only in cross sections) is required. The compatibility of the settlements for the bridge, for the embankment and for the track has to be verified. Figure 6 shows an example of such a joint evaluation with different options of the foundation of the bridge and the embankment and of the construction of the embankment: - raft foundation (case A, C and D); - pile foundation (case B and E); - piled-raft foundation/KPP (case F); - subsoil improvement (case B, D, E and F); - non-stabilized filling material (case A and E); - stabilized filling material (case B, C, D and F). It could be proved, that option F with soil improvement under the embankment, piled-raftfoundation of the abutment and stabilization of the filling of the embankment fulfills the requirements regarding the compatibility of the settlements for the bridge, the embankment and the track and results in a smooth settlement curve without leap.

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Figure 6: Evaluation of the settlements in the transition area from embankment to bridge 5. Conclusions Due to the application of slab (or ballastless) track on the high speed line from Frankfurt to Cologne in Germany, where the above mentioned methods and evaluations have been conducted, the allowed residual settlements and the differential residual settlements have been strictly limited already in the design stage. Therefore a lot of attention has been paid to the filling materials used for the embankments. to the compaction, the dynamic impact and stability and also the settlement prognosis.These evaluations resulted in the above mentioned measures. Finally only preventive grinding of the rails has been necessary for maintenance after the first 3 years of operation (Kocan, 2005), while usually by using ballasted track already extensive tamping is required due to the higher residual settlements during that period. No residual settlements or differential settlements above the limit of generally 15mm after fixing the rails emerged. It is worth to consider the application of these measures also for ballasted tracks in order to reduce maintenance and life cycle costs.

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6. References BetonMarketing Deutschland GmbH (2007): Zementstablisierte Böden Anwendung, Planung, Ausführung. Herausgeber: BetonMarketing Deutschland GmbH. Erkrath, 2007. Cuellar V. et. al. (1999). Mechanical behaviour of a big rockfill highway embankment. Geotechnical Engineering for Transportation Infrastructure, Barends et al. (eds), 1999 Balkema, Rotterdam, ISBN 90 5809 047 7 Dürrwang R., Schulz G., Neidhart Th. (1999). Erdbauwerke für Hochleistunsstrecken. Der Eisenbahningenieur, Heft 8/99. Ehrlinger S. (2006). Bodenstabilisierung mit hydraulischen Bindemitteln. DIB (Deutsches Ingenieurblatt) Special BETON, 03/06. El-Mossallamy Y. (1996). Ein Berechnungsmodell zum Tragverhalten der Kombinierten PfahlPlattengründung. Dissertation im Fachbereich Bauingenieurwesen der TH Darmstadt, 1996. Entenmann W. (2001). Compaction of high dam constructions. 4th International Symposium “Infrastructure Construction Systems and Technologies”, Munich, 6th April 2001. Hecht Th., Lutz B., Dürrwang R. (2001). Wirtschaftlicher Gründungsentwurf für eine Großtalbrücke im Röt. Geotechnik 24, 2001/1. Kliesch K. et al. (2002). Zur Setzungsprognose bei Erdbauwerken mit fester FahrbahnErfahrung an 43 km Neubaustrecke. Vorträge der Baugrundtagung 2002 in Mainz. Kocan D. (2005). Erfahrung mit der Fahrbahn der SFS Köln-Rhein/Main nach Jahren Betrieb. EI-Eisenbahningenieur (56) 11/2005 Kuhl O. (2005). Das neue Merkblatt über Bodenverfestigungen und Bodenverbesserungen mit Bindemitteln. Strasse und Autobahn, 7/2005 Laechler W. (1998). Aufschüttungen für Fahrbahnen mit erhöhten Anforderungen an die Ebenheit. Vorträge der Baugrundtagung 1998 in Stuttgart. Lopez-Pita A. al. (2006). Evaluation of track geometric quality in high speed lines: ten years experience on the Madrid-Seville line. Proc. IMechE Vol. 221 Part F: J. Rail and Rapid Transit, 2007. Nijland T.G. et al. (). Grondstabilisatie met hoogovencement, verhardering and duurzaamheid Schulz G. (1999). Grossversuch im Erdbau hinsichtlich Auswirkungen im Keuper. Vortrag auf der 12. Nationalen Tagung für Ingenieurgeologie, Halle 1999. Schulz G. et. al. (2004). Stabilisierter Erdbau- Erfahrungen auf Neu- und Ausbaustrecken der DB AG. Vortraege der Baugrundtagung 2004 in Leipzig. Stahlmann J.. El-Mossallamy Y. (2001). Die Gründung des Hochhauses Gallileo - innovative wirtschaftliche Lösung oder ingenieurwissenschaftliche Spielerei. Pfahlsymposium TU Braunschweig, 2001. Stahlmann J. (2002). Einsatz Kombinierter Pfahl-Plattengründungen im Verkehrswegebau. VSVI-Seminar Weimar. Tang X., Hu Y. (2009). Erdbautechnische Untersuchungen zur Qualitätssicherung der 1000km langen Hochgeschwindigkeitsstrecke Wuhan – Guangzhou. Bautechnik 86 (2009), Heft 2. Veiga Pinto A., Fortunato E. (1999). The use of soil-rockfill mixtures in the construction of roadfills. Geotechnical Engineering for Transportation Infrastructure, Barends et al.(eds),1999 Balkema, Rotterdam, ISBN 90 5809 0477

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