Time-varying reliability analysis of Majiagou landslide based on weakening of hydro-fluctuation belt under wetting-drying cycles

Abstract

The impoundment of the Three Gorges Reservoir has a significant impact on the storage area, where the frequent occurrence of reservoir landslides with great harm has attracted much attention. Taking the Majiagou landslide as a case, this study focuses on the hydro-fluctuation belt affected by the reservoir operation. Under the scheduling of reservoir water level, the landslide displacement associated with the hydro-fluctuation belt presents a step-like deformation and the movement behaves as a retrogressive type. The wetting-drying cycles test has been performed to simulate the effects of reservoir water level on the hydro-fluctuation belt. Then, the weakening of soil strength parameters is well characterized by an exponential function model. Considering the continuous weakening of the hydro-fluctuation belt, the time-varying reliability, consistent with the actual landslide zoning, is analyzed under the reservoir operation for 10 years. The results indicate that the migration of seepage field in the landslide is closely related to the scheduling of reservoir water level and lags behind the scheduling. Similarly, the factor of safety varies with the reservoir water level, and the minimum value is obtained when the water drops to the lowest level. With the repeated interaction of reservoir water level on the hydro-fluctuation belt, the most dangerous failure probability of the landslide gradually increases. As a result, the stability of the Majiagou landslide declines from the initial basic stable to the less stable state.