Numerical investigation of TBM tunnelling in consolidated clay

Abstract

This study presents a three-dimensional numerical analysis of TBM tunnelling in consolidated clay using the finite element method. An elasto-plastic soil model, based on Mohr-Coulomb criteria, is used in the analysis. An isoparametric quadratic solid consolidation element (IPQC) incorporated in the finite element program FINAL is used for this analysis. The IPQC element has one additional degree of freedom at the corner nodes to represent unknown excess pore water pressure. The governing equations were derived in the light of the generalized Biot theory, where the displacements and the excess pore water pressure are the primary unknowns. An incremental step-by-step analysis is employed to simulate the advance of TBM and its shield and the tunnel construction process. The influence of slurry pressure at the face of the shield and grouting pressure at the tail void gap on the excess pore water pressure is studied. The behaviour of excess pore water pressure mobilization and its dissipation in time is presented. The numerical modelling of construction steps includes the following simultaneous activities: (1) Stepped excavation of soil elements existing in the tunnel region. (2) Step-by-step advance of machine parts by activating and eliminating elements representing TBM and the shield. (3) Activation of elements represents the lining system, where elements of one ring are activated for each step of advance. (4) Stepped activation of elements representing the grouted zone. (5) Time effects are accounted for using an incremental procedure and to allow excess pore water pressure dissipation in each step. To show the impact of slurry pressure and grouting pressure on ground deformations and excess pore water pressure, the proposed numerical technique simulation was employed for TBM tunnelling in clay. The IPQC element was used to model the clay layer, the SHELL element was used to model the shield and the concrete lining. The results of this study show that: (1) Three-dimensional consolidation analysis for the TBM shield tunnelling process is important in order to study the impact of slurry pressure at the face of the shield and grouting pressure at the tail gap on excess pore water pressure. (2) The shape of the excess pore water pressure around the tunnel in the longitudinal and cross-sections and its dissipation in consolidation time are realistic. (3) Excess pore water pressure increases with the increase in slurry pressure. (4) The slurry pressure has a small effect on the vertical displacements of the ground. (5) Increasing grouting pressure increases the excess pore water pressure around the tunnel. (6) The results of this analysis have direct practical significance for optimizing the slurry pressure and the grouting pressure. (A). Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.