Coupled numerical analysis of strain localization induced by shallow tunnels in saturated soils

Abstract

This paper presents an analysis of shallow tunneling in saturated poro-elastoplastic media by means of an enhanced finite element method with strong discontinuities. To perform a fully coupled analysis of the excavation phase, a commonly adopted procedure for the plane simulation of actual three-dimensional tunneling is extended to the case of pervious cavities in saturated media. The enhanced formulation with strong discontinuities shows to be able to capture the onset of strain localization and its propagation from the tunnel up to the ground surface. These results are contrasted with the unsuccessful simulation of localization obtained by the standard finite element method. The comparison shows that the inability of conventional finite elements in reproducing localization can be a reason for unsatisfying predictions of tunneling induced displacements. Furthermore, the influence of the excavation rate on strain localization, on induced displacements and on tunnel stability is thoroughly investigated with the coupled strong-discontinuity method. The calculated response of the saturated soil is also compared to the results of simulations of tunneling in a dry soil, performed with an uncoupled strong-discontinuity formulation and presented in a previous paper.