Tension-shear extension criteria used in PFC2D to reveal a brittle failure of rock bridges in rock slopes with stepped joints

Abstract

Stepped failure is a typical mode in alpine valleys and usually manifests as brittle fractures determined by joints. Tension-shear extension criteria were proposed to reflect the intrinsic mechanism of this failure mode. These criteria combined the theory of linear elastic fracture mechanics and the Mohr-Coulomb (M−C) strength criterion, including propagation trends and fracture conditions, and reflected the fracture behavior of rock bridges determined by joints. The proposed extension criteria were numerically applied in the 2D Particle Flow Code (PFC2D). The mesoscopic strength parameters were calibrated according to a mathematical relationship, which could satisfy the relationship between stress and strength with the proposed criteria. For massive rock slopes dominated by stepped joints, it is determined through theoretical and experimental analysis that rock bridges undergo tensile failure under low normal stress levels, which gives a reasonable explanation of why rock bridges observed in situ generally undergo tensile fracture. The internal mechanism of rock bridge failure is revealed through mechanical analysis of fracture behavior, which is considered in the numerical method. Taking the Xiaowan Hydropower Station as an example, it is confirmed that the simulation results truly reproduce the mesoscopic mechanism of the stepped failure of the slope.