# Stability Analysis of the Huasushu Slope Under the Coupling of Reservoir Level Decline and Rainfall
## 4 Three-Dimensional Slope Stability Analysis
### Analysis of Results of Displacement Simulations  
Figure 15a,b show the horizontal and vertical displacement under Case 1, respectively. In the water-filled state, significant horizontal displacement occurred in the middle and lower parts of the slope mass with values of 0.0002-0.0018 m. The horizontal displacement in other places is relatively small. This was mainly due to the significant deformations of the lower part of the slope caused by the inundation of the slope's anterior border. At the same time, large-scale downward vertical displacement occurred in the middle and upper part of the slope mass with values of 0.004-0.013 m. The displacement direction of the leading edge of the slide is vertically downward, and the displacement value is 0-0.0005 m, mainly due to the steeper upper and middle part of the slide, which makes the landslide produce a large downward vertical displacement under the action of self-weight.  
An analysis of the horizontal displacement cloud maps (Figures 16a, 17a, 18a and 19a) for Cases 1 to 5 shows that the middle and lower parts of the slope mass experienced a certain degree of horizontal displacement in all of the working conditions considered, while the horizontal displacement in other areas was relatively small. When there was no rainfall, the horizontal displacement caused by the drop in the reservoir water level was more significant than that in the underwater storage conditions; i.e., the horizontal displacement under hydrostatic conditions was the smallest. This was because a drop in the reservoir water level changed the surrounding seepage field, increasing the seepage force and sliding force, which increased the horizontal displacement in the slope. After rainfall, the horizontal displacement increased significantly compared with the case without  
Figure 14: (**a**) First principal stress field (kPa) under Case 5. (**b**) Third principal stress field (kPa) under Case 5.  
rainfall, especially in the middle and lower parts of the slope mass, where the horizontal displacement was more significant than at the upper part. This was because rainfall further increased the seepage forces acting within the slope, making the horizontal displacement in Cases 3 and 5 more significant than in in Cases 2 and 4. Case 3 had the largest horizontal displacement with a maximum value of 0.041 m.  
Figure 16: (**a**) Horizontal displacement (m) under Case 2. (**b**) Vertical displacement (m) under Case 2.  
Figure 17: (**a**) Horizontal displacement (m) under Case 3. (**b**) Vertical displacement (m) under Case 3.  
Figure 15: (**a**) Horizontal displacement (m) under Case 1. (**b**) Vertical displacement (m) under Case 1.  
Comparing the vertical displacement maps from Case 2 to Case 5 (Figures 16b, 17b, 18b and 19b) shows that the slip body generates vertical displacement in all cases, and there is a significant change compared with Case 1. The direction of vertical displacement in the middle and upper parts of the slope is downward, and the direction of vertical displacement in the lower part is upward. Under rainfall conditions, the vertical displacement in Cases 3 and 5 is significantly larger than that in Cases 2 and 4 when the reservoir water level drops; especially in Case 3, the vertical downward displacement of the upper and middle parts of the slope body is the largest, reaching 0.05 m, while the vertical upward displacement of the lower part of the slide body is 0.001 m. This is mainly due to the downward slippage of the slope caused by the drop in the reservoir water level, coupled with the combined effect of self-weight and rainfall. This results in the leading edge of the slope being squeezed, thus increasing the slope's size and vertical displacement.