Stability and Failure Mechanism of the Tunnel Face in Nonhomogeneous Clay with Longitudinal Slopes: A Kinematic Limit Analysis: Fid-Bau Portal

Stability and Failure Mechanism of the Tunnel Face in Nonhomogeneous Clay with Longitudinal Slopes: A Kinematic Limit Analysis

Yang, Feng / Qin, Aohan / Zheng, Xiangcou / Yang, Junsheng / Shiau, Jim

Abstract

Longitudinal inclined tunnels are commonly encountered in practical projects, yet limited studies are available on determining the stability of the tunnel face with the presence of longitudinal slopes, especially in nonhomogeneous clay. This study employs the upper-bound finite-element method with rigid translatory moving elements (UB-RTME) to investigate the impact of longitudinal slopes on the stability of tunnel faces and their failure mechanisms. To enhance the computational performance of the UB-RTME, a series of mesh updating and refinement technologies is proposed. Furthermore, this study provides a comprehensive numerical implementation specifically designed for nonhomogeneous clay. By considering combined effects of slope inclination, tunnel burial depth, soil unit weight parameter, and undrained shear strength gradient, compact upper-bound solutions of the load factor $σ_{s} / c_{u 0}$ of the tunnel face are obtained. The associated failure mechanisms, characterized by the meshlike slip surfaces and their evolution, are also determined. Numerical results highlight that both the load factor $σ_{s} / c_{u 0}$ and the failure mechanism of the tunnel face are significantly influenced by the longitudinal slope inclination. Consistent design equations for assessing the stability of the tunnel face are proposed, which can be directly applied in practical scenarios. In addition, the effects of the proposed mesh updating techniques and mesh density on the accuracy of numerical solutions are discussed.