Wedge Stability Analysis In Rock Slope

Wedge failure is one of familiar failure types in rock slope, and the stability analysis of wedge is a classical problem in rock slope engineering. After research findings of the other scholars, the paper advances a new wedge stability analysis method considering anisotropic dilatancy of discontinuities and presents an application of methods introduced in the paper to determine the minimum cover in unlined pressure tunnels.First of all, a brief review of the wedge identification in rock slope is performed. This paper makes an introduction about discontinuities statistic and dominant discontinuities identification with stereographic projection method. After that, we can distinguish the key wedge and its failure type.Secondly, some methods for stability analysis of rock wedge are introduced. They are Traditional Limit Equilibrium (TLE) method, Upper Bound (UB) method based on associated flow rule, General Limit Equilibrium (GLE) method based on Pan's Maximum Principle, the method considering Dilatancy of Discontinuities (DD), and Generalized Solution for Wedge stability analysis (GSW). After contrasting these methods, we find all of them render the wedge stability analysis statically determinate through different methods. These methods are relative to each other. They adopt Mohr-Coulomb failure criterion and treat dilatancy of discontinuities as isotropic in DD & GSW.Thirdly, a new wedge stability analysis method considering anisotropic dilatancy of discontinuity (ADD) for wedge stability analysis is presented in this paper. This method adopts a 3D saw-tooth-like model to characterize the anisotropic dilatancy of discontinuity. The wedge velocity is determined by dilatancy angle of discontinuity, and then, we get the direction of frictional shear force on discontinuity and apparent friction angle. After that, the factor of safety (FS) of wedge comes from static force equilibrium. By contrast with DD & GSW, ADD gets higher FS at the same dilatancy condition. The maximum value of FS gotten from UB, GLE, DD and GSW are defined with isotropic dilatancy.At last, this paper presents an application of methods introduced in the paper to determine the minimum cover in unlined pressure tunnels from the stability of rock wedge. The paper advances two 3D wedge models above the unlined pressure tunnels. The minimum cover criterion can be gotten from the stability of these two wedge models. The Illinois Criterion is a special case of the minimum cover criterion from 3D five-plane wedge model. Dilatancy is suggested to determine the minimum cover in unlined pressure tunnels.