Upper-bound finite element analysis of stability of tunnel face subjected to surcharge loading in cohesive-frictional soil

摘要

The stability of a plane strain tunnel face in a cohesive-frictional soil (idealized as a homogeneously Mohr-Coulomb material) subjected to ground surface surcharge loading was investigated. Continuous loading is applied to the ground surface, and both smooth and rough interface conditions are modeled. The upper-bound solutions with critical load parameters for a practical range of tunnel depth-to-height values, as well as the soil properties, are obtained by using the Upper-bound Finite Element Method with Rigid Translatory Moving Elements (UBFEM-RTME). For practical use, the results are presented in the form of dimensionless stability charts. Failure mechanisms consisting of two groups of slip lines, which explicitly reflect the relative movement of blocks, are also presented. To verify the solutions, the Upper-bound Finite Element Method with Plastic Deformation Elements (UMFEM-PDE) has been developed and the collapsed loads are compared with those from UBFEM-RTME. The solutions obtained with these two upper-bound finite element methods are found to be in good agreement with each other.