Theoretical study on stability evolution of soft and hard interbedded bedding reservoir slopes

Soft and hard interbedded bedding rock slopes, which is prone to failure, are widely distributed in the Three Gorges Reservoir, China. Limit equilibrium method (LEM) is commonly used to analyze the stability of bedding rock slopes that have a single failure plane. However, this method cannot accurately estimate the stability of soft and hard interbedded bedding reservoir slopes because the strength parameters of a soft and hard interbedded rock mass vary spatially along the bedding plane and deteriorate with time due to periodic fluctuations of reservoir level. A modified LEM is proposed to evaluate the stability evolution of soft and hard interbedded bedding reservoir slopes considering the spatial variation and temporal deterioration of shear strength parameters of rock masses and bedding planes. In the modified LEM, the S-curve model is used to define the spatial variation of shear strength parameters, and general deterioration equations of shear strength parameters with the increasing number of wetting-drying cycles (WDC) are proposed to describe the temporal deterioration. Also, this method is applied to evaluate the stability evolution of a soft and hard interbedded bedding reservoir slope, located at the Three Gorges Reservoir. The results show that neglecting the spatial variation and temporal deterioration of shear strength parameters may overestimate slope stability. Finally, the modified LEM provides useful guidance to reasonably evaluate the long-term stability of soft and hard interbedded bedding reservoir slopes in reservoir area.