Study on the mechanisms of flexural toppling failure in anti-inclined rock slopes using numerical and limit equilibrium models

Flexural toppling failure (FTF) is one of the main types of toppling failures and frequently occurs in anti-inclined rock slopes. A new UDEC Trigon approach for simulating FTF of a model slope was presented in this paper. FTF of anti-inclined rock slopes characterized by tensile failure of rock columns was successfully captured with the new method. Subsequently, special effort was made to investigate the effects of joint cohesion and joint friction angle on flexural toppling movements' mechanisms. Furthermore, a limit equilibrium method, which can reflect the effects of the joint cohesion, was proposed to quantitatively evaluate the stability of anti-inclined rock slopes against FTF. The results demonstrate that the deformation process of FTF can be divided into three stages: elastic deformation due to cohesion, development of FTF after interlayer slip, and formation of the total failure surface. The inter-column normal forces will suddenly decrease when the failure surface begins to initiate inside the slope, which can be regarded as an instability indicator of anti-inclined rock slopes against FTF. Joint cohesion and joint friction angle were found to have significant effects on the stability of anti-inclined rock slopes, but make an insignificant impact on the shape, location, and formation process of the failure surface. The simulated results indicate that joint cohesion should be considered when using the limit equilibrium method to evaluate the stability of anti-inclined rock slopes against FTF. Inaccurate result will be predicted if the joint cohesion is neglected in the limit equilibrium method.