## 4 Result
### Stability of the Landslide
This decrease in pore water pressure results in an increase in the effective stress of the soil mass, consequently enhancing its effective shear strength. However, the declining water level has also caused a reduction in the pressure acting on the landslide surface and directed towards the interior of the landslide, as well as a decrease in the normal stress acting at the base of the sliding mass. These reductions have contributed to an increase in the instability factors of the landslide, leading to a substantial decrease in landslide stability as the reservoir water level decreases. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Water Level Status** & **Groundwater + Reservoir Level** &
\begin{tabular}{c} **Groundwater + Reservoir Level** \\ **+ Rainfall** \\ \end{tabular} \\ \hline Normal water level & 1.062 & 1.062 \\ Dead water level & 1.048 & 1.048 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Landslide safety coefficients at different reservoir levels. Figure 15: Saturation maps at varying water levels. During April 2019 and April 2022, the of the Guangdong Reservoir experienced frequent water-level fluctuations. To further explore the temporal evolution of the stability of the reservoir bank landslide, the water level and rainfall intensity data measured during this period were input into a numerical model in Geostudio for computational analysis. Figure 17 illustrates the temporal variation of the landslide factor of safety. It is evident that there is a strong correlation between the stability of the reservoir bank landslide and the reservoir water level. As the reservoir water level rises and falls, the landslide safety coefficient also increases and decreases accordingly. The greater the fluctuation in reservoir water level, the larger the range of change in the safety coefficient. Under the coupling effect of actual reservoir water level changes and rainfall, the safety coefficient of the reservoir bank landslide is almost identical to that under the condition considering only the effect of reservoir water level changes. This further indicates that the impact of rainfall on the stability of the reservoir bank landslide is minimal, consistent with previous computational results. To further investigate the influence of reservoir water level change rates on landslide stability, we conducted an analysis of the stability of reservoir bank landslides under varying rates of reservoir water level rise and fall. In actual conditions, the maximum rate  
Figure 16: The distribution of pore water pressure and total pressure on the sliding surface at different reservoir water levels. Figure 17: The temporal variation of the landslide factor of safety. of reservoir water level decline is approximately 2 m/day. We considered four different scenarios of reservoir water level change: 0.5 m/day, 1 m/day, 1.5 m/day, and 2 m/day. Initially, the reservoir water level was maintained at the normal level for 0-35 days, after which it was lowered to the dead water level at different rates. This level was maintained for a period until the pore water pressure stabilized (147 days), after which the reservoir water level was raised back to the normal level at the same rate as the reservoir water level had dropped. Figure 18 depicts the variations in landslide safety factors under different rates of reservoir water level change. It reveals a nearly one-to-one correspondence between the landslide safety factor of this project and the elevation of the reservoir water level. The safety factor changes synchronously with the reservoir water level changes, without exhibiting any lag in response to the water level variations. The rate of safety factor change is not uniform, with the fastest changes occurring at the beginning of the reservoir water level decline and at the end of the reservoir water level rise. Figure 18: Evolution of landslide stability under different rates of reservoir level change: (**a**) the evolution of safety factor over time; (**b**) change rate of safety factor over time.