Three-dimensional face stability of shallow-buried tunnels with tensile strength cut-off

Abstract

In terms of a very small or even zero tensile strength of soils, the tensile strength cut-off is introduced to modify the classical Mohr-Coulomb failure criterion which allows a nonlinear strength envelope of soils in tensile regime. Based on the modification, an improved three-dimensional (3D) rotational failure mechanism is proposed to assess the face stability of a soil tunnel in the framework of limit analysis. The shallow-buried case is investigated to account for the influence of tensile strength cut-off on face stability of tunnels with different buried-depths. The influences of the unit weight of soils γ, the ratio ξ, the cohesion c and the internal friction angle φ on the critical support pressure are researched using the proposed approach. In order to assess the face stability of tunnels under water table, the coefficient ru is employed to describe the distribution of pore water pressure. It is found that the proposed approach can give a more critical support pressure against tunnel face failure, and the presence of pore water pressure makes the influence of tensile strength cut-off more prominent.