## 5 Conclusions  
In this paper, a fluid-structure coupling numerical simulation analysis is carried out for the landslide phenomenon of a reservoir project's left bank high slope. The influence of formation lithology, fault, excavation unloading, rainfall, and water storage is comprehensively considered to explain the failure mechanism of the slope under the action of excavation unloading and heavy rain. The main conclusions are as follows:  
1. With the extension of rainfall time, saturation increases, pore water pressure increases, and matrix suction in shallow soil decreases or disappears. After rainfall decreases or stops, saturation decreases gradually with the extension of time, pore water pressure drops, and matrix suction in the shallow soil layer increases slowly.
2. Under the action of excavation unloading, the high slope rebounds and deforms, resulting in a loose structural plane at fault F1 at the back edge of the excavated slope. Under the action of rainfall infiltration, saturation in the structural plane increases, and pore water pressure increases. With rainfall infiltration, the shear strain concentration area first appears at the inner structural plane of the slope. It extends along the structural plane to the front and rear edges of the slope, resulting in landslide failure of the slope.
3. For the typical structural plane-controlled slope, excavation unloading deformation is mainly represented by structural plane deformation. The slope deformation is composed chiefly of the structural plane dislocation deformation. Structural plane deformation is primarily controlled by the exposure of the structural plane when excavating the free face, excavation unloading scale, etc. The shear failure and unstable displacement caused by excavation unloading are the leading causes of landslides.
4. The unloading deformation of slope excavation is mainly manifested as the deformation of the structural plane, and the slope deformation is composed chiefly of the dislocation deformation of the structural plane. The deformation of the structural plane is mainly controlled by the exposure of the structural plane in excavating the free surface and the scale of excavation unloading. In practical applications, load-reduction measures can be used to improve the stability of the slope.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Model Type** & **Calculated Safety Factor** & **Tolerable Safety Factor** \\ \hline Original model & 1.09 & 0.5 & 1.35 \\ First Excavation Model & 1.10 & 4.5 & 1.35 \\ Second Excavation Model & 1.27 & 3.5 & 1.35 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Strength parameters of slope materials.  
**Author Contributions:** Conceptualization, M.Q. and F.D.; methodology, M.Q.; software, M.Q.; validation, M.Q. and F.D.; formal analysis, M.Q.; investigation, M.Q.; resources, M.Q.; data curation, M.Q.; writing--original draft preparation, M.Q.; writing--review and editing, M.Q.; visualization, M.Q.; supervision, F.D.; project administration, F.D.; funding acquisition, F.D. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was supported by the National Natural Science Foundation of China (No. 51979225).  
**Data Availability Statement:** The dataset used to support the findings of this study is available from the corresponding author upon request.  
**Conflicts of Interest:** The authors declare that there is no conflict of interest.