Failure analysis of tunnel face influenced by overload and longitudinal slope

Aiming at the stability of excavation face of tunnels under the influence of surface overload and longitudinal slope, an initial triangular mesh updating strategy derived from the structural failure mechanism is proposed. The computation is conducted by using the upper bound method with the rigid translatory moving elements (UB-RTME) with nonlinear programming to generate stability charts for the load factor σ_s/c and obtain the slip line failure modes. The results show that the range affected by the failure modes and the major failure domain are given by both the UB-RTME slip line mesh and the Optum G2 adaptive encryption mesh. The range of failure area is determined by the effective discontinuities and element velocity characterized by the UB-RTME. The quantitative data of the failure area S/D² and the relationship between the slip line failure modes and the influencing factors are provided. The load factor σ_s/c decreases significantly with the increase of the longitudinal slope angle θ, increases with the increasing buried depth ratio C/D. It decreases with the increase of the gravity coefficient γD/c while increases nonlinearly with the increase in the internal friction angle ϕ. For the case with large values of C/D and ϕ, the mesh density will significantly affect the accuracy of the σ_s/c numerical solution obtained by the UB-RTME operation. With the increase of the mesh density, the accuracy of the calculated results of σ_s/c is significantly improved, and the slip line reflecting the failure characteristics becomes smoother.