Three-dimensional finite element analysis of earth pressure balance tunnelling

Abstract

This study investigates the viability of applying three-dimensional finite element analyses to the prediction of ground movement arising from earth pressure balance tunnelling. It seeks to address two of the issues involved in three-dimensional finite element analysis through firstly the feasibility of conducting three-dimensional analysis without resorting to inordinate amounts of computer resources and time and secondly the usefulness of three-dimensional analysis in predicting field movement and its advantages compared to two-dimensional analysis.Krylov subspace iterative solvers namely element-by-element Preconditioned Conjugate Gradient (PCG) and Quasi-Minimal Residual (QMR) were examined over the direct method of solving stiffness matrix arising from geotechnical domains. The performance of the Jacobi Preconditioner when used with these iterative methods was shown to be different for drained, undrained and consolidation problems, even for similar condition number. The differences were due to the eigenvalue distribution.The second issue was address through through a back-analyse in an actual three-dimensional tunnel heading problem. Important parameters such as excavation step length, drainage boundary conditions, face pressure and non-linear small strain soil model were found to be affecting the ground response significantly.A graphical approach depending on tunnel standoff position was crafted to depict two-dimensional ground loss to the three-dimensional ground responses.