# Stability Analysis of the Huasushu Slope Under the Coupling of Reservoir Level Decline and Rainfall
## 1 Introduction  
China has been prone to geological disasters since ancient times due to its complex and diverse terrain, geological conditions, and climate types. The Three Gorges reservoir area, China's largest hydropower project, has played an essential role in flood control and power generation since its construction. However, the unique geological and climatic conditions of the reservoir area pose many risks of geological disasters. To study geological disasters in this area and their impact on slope stability, substantial in-depth research has been conducted on landslides and collapse formation mechanisms. The main factors affecting the stability of reservoir slopes include rainfall, reservoir water level fluctuations, the physical and mechanical properties of the rock-soil mass, and human activities. Studies have reached consistent conclusions that fluctuations in reservoir water levels significantly impact slope stability. Japanese studies have shown that about 60% of reservoir landslides occur after sudden drops in reservoir water levels. In comparison, 40% occur during rises in water levels, especially during the initial filling of the reservoir [1]. Thisindicates that water level fluctuations--especially rapid drops--can have a significant impact on slope stability. [PERSON] et al. [1; 2; 3] verified that the rate of water level drop is negatively correlated with the stability coefficient: the faster the drop, the more obvious the decrease in the stability coefficient. This is due to a drastic change in pore water pressure, reducing the shear strength. [PERSON] et al. [4] determined the instability mechanism for the slope of a bank on a dichotomous structure through a physical model of water level rising and falling using a monitoring technique. In terms of theoretical and numerical analyses, [PERSON] [5] used the [PERSON] model to calculate the slope stability of a pit lake and showed that a decreased water level reduces slope stability. [PERSON] et al. [6; 7] used unsaturated seepage theory to confirm the significant effect of the water level's rate of change on the coefficient of safety. Based on this theory, [PERSON] et al. [8] proposed a dynamic analysis framework of seepage force to analyze the effect of water level decline on slope stability, quantitatively assessing stability pairs under precipitation conditions. [PERSON] et al. [9] found that a larger unsaturated zone improves slope stability. [PERSON] et al. [10; 11; 12] verified the stability of three slopes based on the Morgenstern-Price method and the Bell algorithm, verifying the reliability of this slope analysis method for the Three Gorges reservoir area. [PERSON] et al. [13] analyzed the effect of reservoir water level drops on slope stability using a finite element model, emphasizing the effect of the transient seepage field on the slope. In addition, as another predisposing factor, rainfall is closely related to slope deformation. [PERSON] et al. [14] analyzed rainfall data from severely affected areas through optical and radar data analysis, and showed that rainfall action is also a major predisposing factor for slope deformation. This further confirmed the mechanism of landslide instability under the action of multiple factors. [PERSON] et al. [15] used Automatic Dynamic Incremental Nonlinear Analysis (ADINA)-Structure software (V1.0) to show that high-intensity rainfall increases the bottom movement of slopes. [PERSON] et al. [16; 17; 18] showed that slopes are susceptible to instability under intense rainfall through numerical modeling. Regarding coupling effects, [PERSON] et al. [19] coupled snow melting with rainfall, finding that increased water content under the influence of rainfall decreases the safety factor in the snow melting stage. [PERSON] et al. [20] combined seepage force with the limit equilibrium method to construct a multifactor dynamic prediction model. [PERSON] et al.