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The Interaction Between Shield, Ground and Tunnel Support in TBM Tunnelling Through Squeezing Ground

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The Interaction Between Shield, Ground and Tunnel Support in TBM Tunnelling Through Squeezing Ground CORE Metadata, citation and similar papers at core.ac.uk Provided by RERO DOC Digital Library Rock Mech Rock Eng (2011) 44:37–61 DOI 10.1007/s00603-010-0103-8 ORIGINAL PAPER The Interaction Between Shield, Ground and Tunnel Support in TBM Tunnelling Through Squeezing Ground M. Ramoni • G. Anagnostou Received: 15 January 2010 / Accepted: 14 May 2010 / Published online: 15 June 2010 Ó Springer-Verlag 2010 Abstract When planning a TBM drive in squeezing C Circumference ground, the tunnelling engineer faces a complex problem Cce Arc length of the deformable concrete elements involving a number of conflicting factors. In this respect, Csc Arc length of the shotcrete ring numerical analyses represent a helpful decision aid as they Css Circumference of the steel set provide a quantitative assessment of the effects of key D Boring diameter parameters. The present paper investigates the interaction d1 Thickness of the shotcrete layer between the shield, ground and tunnel support by means of d2 Height of the deformable elements (yielding computational analysis. Emphasis is placed on the bound- support) ary condition, which is applied to model the interface e Extrusion rate of the core between the ground and the shield or tunnel support. The E Young’s modulus of the ground paper also discusses two cases, which illustrate different Esc Young’s modulus of the shotcrete methodical approaches applied to the assessment of a TBM Ess Young’s modulus of the steel drive in squeezing ground. The first case history—the F Thrust force Uluabat Tunnel (Turkey)—mainly involves the investiga- Fb Boring thrust force tion of TBM design measures aimed at reducing the risk fc Uniaxial compressive strength of the ground of shield jamming. The second case history—the Faido fc,ce Maximum compressive stress of the deformable Section of the Gotthard Base Tunnel (Switzerland)—deals concrete elements with different types of tunnel support installed behind a fc,sc Uniaxial compressive strength of the shotcrete gripper TBM. fy,ss Yield stress of the steel Fi Installed thrust force Keywords Tunnel boring machine Á fl Boundary condition for the simulation of the Mechanized tunnelling Á Squeezing ground Á tunnel support Shield jamming Á Tunnel support Á Yielding support Á Fr Required thrust force Numerical investigation Á Steady state method fs Boundary condition for the simulation of the shield H Depth of cover Abbreviation K Stiffness of the lining A Cross-sectional area of the steel set l ss K Stiffness of the shield b Steel set spacing s l Length of a critical geological zone b0 Steel set clear distance L Length of the shield c Cohesion of the ground N Hoop force Nce Hoop force in the deformable concrete elements n Number of deformable concrete elements M. Ramoni (&) Á G. Anagnostou ce ETH Zurich, Zurich, Switzerland Nf Friction loop resistance e-mail: [email protected] nf Number of friction loops 123 38 M. Ramoni, G. Anagnostou Nmax Yield load of the steel set convergences of the bored profile, damage to the tunnel Nsc Hoop force in the shotcrete ring support). ‘‘Squeezing’’ refers to the phenomenon of large Ny Yield load of the sliding connections long-term deformations of the bored profile due to the p Ground pressure overstressing of the ground surrounding the tunnel. It ps Average ground pressure acting upon the shield occurs mostly in weak rocks with a high deformability and r Radial co-ordinate (distance from the tunnel axis) a low strength and often in combination with a high R Tunnel radius overburden and a high water pressure (Barla 2001; Kova´ri RF,T Reaction force 1998). Phyllites, schists, serpentinites and claystones are s Step length (step-by-step calculations) among the rocks often exhibiting heavily squeezing t Time behaviour. As experienced, e.g., in some stretches of the T Torque Gotthard Base Tunnel (Switzerland), relevant deformations u Radial displacement of the ground (at the tunnel for TBM tunnelling may occur also in relatively hard but boundary) fractured rocks (e.g., gneisses), particularly if encountered ul Radial displacement of the lining at great depths. v Advance rate An extended review of the literature concerning expe- y Axial co-ordinate (distance behind the tunnel rience with TBMs in squeezing ground, the possible tech- face) nological improvement of the common TBM types (i.e., y0 Position of the tunnel face gripper, single and double shielded TBM), the develop- DR Radial gap size ment of alternative machine concepts, the possible mea- ess,max Failure strain of the steel sures for coping with squeezing ground and the et Hoop strain development of deformable lining systems that might cope et,ce Hoop strain of the deformable concrete elements better with high ground pressures can be found in Ramoni et,sc Hoop strain of the shotcrete and Anagnostou (2010b). et,ss Hoop strain of the steel set When evaluating the feasibility of a TBM drive in u Angle of internal friction of the ground squeezing ground, it is of paramount importance to l Shield skin friction coefficient understand the mechanisms governing the interaction m Poisson’s ratio of the ground between shield, ground and tunnel support. For the design r Stress of the TBM and the tunnel support, a series of issues must p r0 Initial stress be investigated in relation to the ground pressure (acting r1 Maximum principal stress upon the cutter head, the shield and the lining), the con- u r3 Minimum principal stress vergence of the tunnel wall , the extrusion rate of the e F T rrr Radial stress core , the required thrust force and the torque as well R rry Shear stress as the resulting reaction forces F,T (Fig. 1). All of these v rt Hoop stress parameters may also depend on the advance rate or on the rt,ce Hoop stress in the deformable concrete elements duration of any excavation standstill that may take place. rt,sc Hoop stress in the shotcrete A number of different analytical, empirical and numer- rt,ss Hoop stress in the steel set ical approaches have been proposed in the literature for the rtt Tangential stress quantitative assessment of these parameters (Sect. 2). The ryy Axial stress present paper follows a numerical approach, addressing the w Dilatancy angle of the ground question of the boundary conditions that need to be applied in order to simulate the interface between ground and shield or tunnel support adequately (Sect. 3) and discussing the structural interplay between these system components by means of computational results (Sect. 4). The paper also 1 Introduction presents two examples of real world applications which illustrate possible methodical approaches to the assessment Squeezing ground represents a challenging condition for of a TBM drive in squeezing ground (Sects. 5, 6). The first operating tunnel boring machines (TBMs), because even case history—the Uluabat Tunnel (Turkey)—mainly con- relatively small convergences of up to 10–20 cm (that cerns the investigation of TBM design measures with the would not really be problematic in conventional tunnelling) aim of reducing the risk of shield jamming. The second may lead to difficulties in the machine (sticking of the case history—the Faido Section of the Gotthard Base cutter head, jamming of the shield) or in the back-up area Tunnel (Switzerland)—deals with the different types of (e.g., jamming of the back-up equipment, inadmissible tunnel support installed behind a gripper TBM. A 123 The Interaction between Shield, Ground and Tunnel Support 39 Fig. 1 Critical parameters for a gripper TBM (a) and a single shielded TBM (b) in squeezing ground considerable degree of engineering judgement is required who developed design charts for the operability of double in cases such as this—in contrast to shielded TBMs where shielded TBMs in gripper mode, as well as by Vigl et al. the support is, as a rule, pre-determined (precast segmental (1999) in their discussion of the latest developments in lining). double shielded TBMs. On the basis of numerical calcu- lations, Ga¨rber (2003) improved the convergence-confine- ment method, provided charts for the design of deep 2 Design and Analysis Methods tunnels in low permeability saturated porous media and applied the proposed semi-analytical solution method to 2.1 Closed-Form Solutions the back-analysis of the segmental lining for the Nuclear Research Centre Connecting Gallery (Belgium), which was The method of characteristic lines is the simplest and excavated by a single shielded TBM (D = 4.81 m). widely used analysis method in tunnelling. It has also been used by Kova´ri (1986a, b) with respect to some of the 2.2 Empirical Relationships issues of TBM tunnelling in squeezing ground. Vogelhuber (2007) later applied the convergence-confinement method Other studies have attempted to get around the drawbacks for investigating the crossing of a shear zone at great depth of analytical solutions by introducing empirical functions with a double shielded TBM of 10 m diameter. He was based upon field measurements, which describe the longi- thereby able to differentiate between the short-term and tudinal distribution of the radial displacement of the tunnel long-term behaviour of the ground. The method of char- boundary. Schubert (2000) showed the effect of the acteristic lines is still used today for analysing the inter- advance rate on tunnel closure in a specific case using the action between ground and support also with regard to relationships proposed by Sulem et al. (1987) and deformable segmental linings of shield-driven tunnels improved by Sellner (2000). Farrokh et al. (2006), Jafari through squeezing rock (cf., e.g., Billig et al. 2007; et al. (2007) and Khademi Hamidi et al. (2008) evaluated Schneider and Spiegl 2008).
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