The Toppling Deformation and Failure Criteria of a Steep Bedding Rock Slope—The Case of a Bank Slope at the Duonuo Hydropower Station

In this study, statistical analysis was conducted to categorize a large number of actual typical cases and analyze the formation conditions of toppling deformation in bedding rock slopes. Based on geological prototypes and similarity theory, a bottom friction test was conducted on the toppling deformable body while considering the excavation process. Based on the deformation and failure phenomena observed in the bottom friction test model, along with the displacement curves at key points, the deformation process in steep bedding rock slopes can be divided into the following five distinct stages: the initial phase, the unloading–rebound phase, the tensile failure phase, the bending creep phase, and the bending–toppling damage phase. To evaluate the stability, a new constitutive model of the nonlinear viscoelastic–plastic rheology of rock masses was developed. This model is based on a nonlinear function derived from analyzing the creep test data of rock masses under fractional loading. Furthermore, a mechanical equilibrium differential equation for rock slabs was formulated to quantitatively describe the aging deformation and failure processes of slopes with delayed instability. Finally, a stability criterion and a quantitative evaluation model for toppling deformation slopes that considered time-varying factors were established. The stability of the model was calculated using a hydropower station slope case, and the results were found to be in good agreement with the actual situation.