Upper-Bound face stability analysis of rectangular shield-driven tunnels in undrained clays

Abstract

The face stability of rectangular shield-driven tunnels in undrained clays where the undrained shear strength increases linearly with depth is investigated numerically and analytically in this paper. In the framework of the kinematic approach of limit analysis, two new failure mechanisms based on the translational movement of rigid blocks and continuous deformation of soil mass are proposed for collapse and blowout cases. The analytical solutions of the failure mechanisms were compared with those of finite element simulations and the existing approaches in the literature to evaluate their validity and productivity. The critical support pressures obtained from the analytical models are relatively consistent with the results of the numerical simulations for square and wide rectangular tunnels. Simple design formulas were provided for analytical models to compute the limit support pressure for practical use. Finally, parametric studies were performed to explore the impact of different geometrical and geotechnical parameters pertaining to the stability of the tunnel face.