Time-Varying Reliability Analysis of the Majiagou Landslide

Rainfall and reservoir water level (RWL) fluctuations are the most important factors affecting reservoir landslide stability. Although extensive research has explored landslide stability under the combined effect of rainfall and RWL fluctuation, quantitative investigations on the individual contributions of rainfall and RWL fluctuation to landslide stability are limited. To address this issue, taking the Majiagou landslide in the Three Gorges Region (TGR) as an example, the seepage field of the Majiagou landslide was simulated and analyzed under three different scenarios: the individual effect of rainfall; the individual effect of RWL fluctuation; and the combined effect of rainfall and RWL fluctuation. The corresponding stability condition of the three scenarios was evaluated. The results show that the fluctuation of RWL is the critical factor that governs the stability of the Majiagou landslide. Specifically, when the water level drops rapidly from 165 m to 145 m, with an average rate of 0.859 m/d, the landslide safety factor decreases most significantly. The reason is that rapid water level decline creates outward-directed seepage forces that promote slope deformation. In contrast, rainfall has a limited effect on slope stability, with the safety factor only decreasing when rainfall exceeds 50 mm/d. This is because a seepage force directed outward from the slope develops only when rainfall reaches a certain threshold, leading to a reduction in the slope’s safety factor. In addition, this study reveals that the combined effect of rainfall and RWL fluctuations generates a synergistic amplification mechanism. Specifically, the safety factor variation under combined hydrological conditions significantly exceeds the arithmetic sum of individual rainfall-induced variation and RWL-induced variation. This study helps us understand how rainfall and RWL fluctuation affect slope stability by altering the seepage field, which is crucial for preventing landslides.