Squeezing loading of segmental linings and the effect of backfilling

https://doi.org/10.1016/j.tust.2011.05.007Get rights and content

Abstract

Overstressing of the segmental lining is one of the major hazard scenarios related to shielded TBM tunnelling in squeezing ground. The present paper deals with this specific problem, addressing the key question of the ground pressure acting upon a segmental lining installed behind a single shielded TBM. Starting with a structured discussion of the influencing factors and their interactions, the paper investigates how the type, location and thickness of the backfilling play an important role with respect to the loading of a segmental lining. Secondly, it explains how to take due account of the actual thickness of the backfilling (which is not known a priori since it depends on the deformations of the bored profile) in a numerical simulation. Thirdly, the paper advances a number of theory-based decision aids which cover the relevant range of ground parameters, initial stress, segmental lining and backfilling characteristics, thus supporting rapid initial assessments of the ground pressure acting upon a segmental lining and making a valuable contribution to the decision-making process.

Highlights

► Structured discussion of the factors influencing the loading of a segmental lining. ► Numerical simulations which take account of the actual thickness of the backfilling. ► Dimensionless nomograms for the assessment of the loading of a segmental lining.

Introduction

The main hazard scenarios for shielded TBM tunnelling in squeezing ground are sticking of the cutter head, jamming of the shield or damage to the tunnel support. Furthermore, the occurrence of significant deformations (ovalization) or even horizontal or vertical shifting of the segmental lining may lead to jamming of the back-up equipment or to violation of the clearance profile.

In a series of recent publications, the authors discussed the specific problems of – and experience with – TBMs in squeezing ground, reviewed the available countermeasures, commented on possible technological improvements (including the development of deformable lining systems), analyzed the interaction between the shield, ground and tunnel support quantitatively and provided design charts concerning the thrust force needed in order to avoid shield jamming (Ramoni and Anagnostou, 2010a, Ramoni and Anagnostou, 2010b, Ramoni and Anagnostou, 2010c, Ramoni and Anagnostou, 2010d). The present paper extends this research by addressing the potential hazard of lining overstressing.

A realistic estimation of the loading of a segmental lining is only possible if due account is taken of the backfilling features. Section 2 of the present paper shows – with a structured discussion of the influencing factors and their interactions – that the type, location and thickness of the backfilling play an important role with respect to the ground pressure acting upon a segmental lining. Section 3 explains how to take due account of these features in a numerical simulation and, more specifically, how to deal with the non-linearity of the problem. The problem is demanding because the actual thickness of the backfilling is not known a priori, as it depends on the ground deformations that occur between the tunnel face and the point at which the backfilling is completed. Section 4 presents, in the form of dimensionless design nomograms, the results of a comprehensive parametric study into the ground pressure acting upon a segmental lining which exploits the numerical efficiency and reliability of the computational model introduced in Section 3. The nomograms cover the relevant range of ground parameters and initial stress, as well as different characteristics of the TBM, the segmental lining and the backfilling (type and location), and allow a quick preliminary assessment to be made of the loading of a segmental lining. This is the first time that such a systematic and thorough investigation has been presented.

An extended literature review on computational methods for TBM tunnelling in squeezing ground can be found in Ramoni and Anagnostou (2010b). Recent publications closely related to the topic of the present paper include those of Simic, 2005, Graziani et al., 2007 and Schmitt (2009). Simic (2005) carried out numerical investigations for the assessment of the loading of the segmental lining in the “La Umbria” Fault of the Guadarrama Tunnel (Spain, double shielded TBM, D = 9.51 m), taking into account the effect of creep. Graziani et al. (2007) investigated a double shielded TBM drive (D = 11.00 m) for the planned Brenner Base Tunnel (Austria/Italy) in the framework of the “TISROCK” research project, gaining a valuable insight into the effects of the length of a shear zone and of the stiffness of the backfilling on the sectional forces in the segmental lining. The work of Schmitt (2009) is of a more general nature and investigates the effects of non-uniform convergence and of non-hydrostatic shield and lining loading for single shielded TBMs. All of these investigations are based upon fully three-dimensional, step-by-step numerical simulations, assuming a priori the thickness of the backfilling and, consequently, the stiffness of the tunnel support. As will be shown later in the present paper, this simplification is unavoidable when using the commonly available computational codes. Furthermore, it leads to a major reduction in the computational effort (particularly when carrying out parametric studies).

Section snippets

Dimensionless parameters

The main result of the numerical computations is the final value of the ground pressure far behind the tunnel face. Fig. 8, Fig. 9, Fig. 10c show typical load distributions p(y) along the tunnel.

The ground pressure p acting upon the segmental lining depends on the material constants of the ground (Young’s modulus E, Poisson’s ratio ν, uniaxial compressive strength fc, angle of internal friction φ and dilatancy angle ψ), on the initial stress σ0, on the characteristics of the TBM (tunnel radius R

Closing remarks

When evaluating the feasibility of a shielded TBM drive in squeezing ground, one of the key questions to be addressed concerns the loading of the segmental lining. Therefore, as shown in Section 2, it is important to take due account of the type, location and actual thickness of the backfilling of the segmental lining.

Computational investigations provide valuable indications as to the magnitude of the ground pressure. In this respect, simplified investigations by means of the

Acknowledgements

This paper evolved within the framework of the research project “Design aids for the planning of TBM drives in squeezing ground”, which is being carried out at the ETH Zurich, supported by the Swiss Tunnelling Society (STS) and financed by the Swiss Federal Roads Office (FEDRO).

References (26)

  • M. Ramoni et al.

    Thrust force requirements for TBMs in squeezing ground

    Tunnelling and Underground Space Technology

    (2010)
  • M. Ramoni et al.

    Tunnel boring machines under squeezing conditions

    Tunnelling and Underground Space Technology

    (2010)
  • Anagnostou, G., 1992. Untersuchungen zur Statik des Tunnelbaus in quellfähigem Gebirge. Veröffentlichungen des...
  • Anagnostou, G., 2007. The one-step solution of the advancing tunnel heading problem. In: ECCOMAS Thematic Conference on...
  • G. Anagnostou et al.

    Significant parameters in elastoplastic analysis of underground openings

    Journal of Geotechnical Engineering

    (1993)
  • Boldini, D., Graziani, A., Ribacchi, R., 2000. L’analisi tensio-deformativa al fronte di scavo e nella zona del...
  • L. Cantieni et al.

    On the variability of squeezing in tunnelling

  • L. Cantieni et al.

    The effect of the stress path on squeezing behaviour in tunnelling

    Rock Mechanics and Rock Engineering

    (2009)
  • L. Cantieni et al.

    On a paradox of elasto-plastic tunnel analysis

    Rock Mechanics and Rock Engineering

    (2010)
  • A. Graziani et al.

    Practical estimate of deformations and stress relief factors for deep tunnels supported by shotcrete

    Rock Mechanics and Rock Engineering

    (2005)
  • A. Graziani et al.

    Analysis of rock-TBM-lining interaction in squeezing rock

    Felsbau magazine

    (2007)
  • K. Kovári

    Tunnelling in squeezing rock

    Tunnel

    (1998)
  • Kovári, K., Anagnostou, G., 1995. The ground response curve in tunnelling through short fault zones. In: 8th Congress...
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    Formerly: ETH Zurich, Switzerland.

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