## 5 Conclusions  
In this study, the slope stability of an open-pit mine discharge site under the influence of wetting-drying cycles in the rainy season in the Cao Son open-pit mine, in the Cam Pha area of Vietnam, was investigated. Experiments on the physical properties of the rock body under different numbers of wetting-drying cycles were carried out, the flow-solid coupling secondary development process and the numerical simulation scheme of wetting-drying cycles were established, numerical analyses were carried out, and some \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Number of Cycles** & **0** & **1** & **2** & **3** & **4** & **5** \\ \hline Factor of Safety & 1.721 & 1.476 & 1.213 & 1.107 & 1.083 & 1.055 \\ \hline Discount Rate & 0\% & 14\% & 18\% & 9\% & 2\% & 3\% \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Waste dump slope factor of safety at different numbers of wetting–drying cycles. meaningful conclusions were obtained. The results show that the cohesion of the slope rock body slowly decreases with the number of wetting-drying cycles, the angle of friction changes less, and the permeability coefficient increases, stabilizes and finally decreases with the number of wetting-drying cycles. With the wetting-drying cycles, the maximum positive pore water pressure on the slope surface and the maximum negative pore water pressure in the slope body become larger and larger. The slope showed a transient saturated zone, and the range of the unsaturated zone decreased with the increase in the number of wetting-drying cycles. The saturation line shifted downward faster in the pre-inflation period due to the dryness of the soil body of the drainage field, and it then decreased with the wetting-drying cycles. After each rainfall event, the range of the rainfall impact area was always larger than the range of the transient saturated area, and with the rainfall cycle, the range of the impact area became larger. The peak slope displacement increased with the number of wetting-drying cycles, and the range of slope displacement and maximum shear strain increment decreased with the number of wetting-drying cycles. This effect was finally focused on the single-step slopes, and the landslide pattern of the slopes reflected a shallow landslide. The slope stability of the Bang Nau dump slope decreased by about 39 percent under the condition of multiple rainfall events in the area with five wetting-drying cycles, and the landslide pattern also changed from a monolithic landslide to a single-stage shallow landslide. Although still in a stable state, the slope has a certain risk of surface shallow landslide damage after many wetting-drying cycles. In order to reduce the impact of wetting-drying cycles on the dump, the material with a smaller block size and permeability coefficient should be discharged to the surface of the slope, and the top of the slope rock and soil should be compacted. It is necessary to strengthen the inspection and slope monitoring during the rainy season, aiming to stop mining activities and redesign the slope if abnormal slope conditions are found. Due to the limited research topic and the space limitations in this paper, more wetting-drying cycle experiments and numerical analyses are required in in-depth research. Moreover, the acidity and alkalinity of rainwater, the temperature and other factors involved in the wetting-drying cycles have not been taken into account, so these factors will be further studied in the future. Conceptualization, Y.W. and V.S.B. ; methodology, V.S.B. ; software, Y.W. ; validation, Z.A. and X.L. ; formal analysis, D.N. ; investigation, T.V. ; resources, H.P. ; data curation, H.N. ; writing--original draft preparation, Y.W. ; writing--review and editing, V.S.B. ; visualization, Z.A. ; supervision, W.Z. ; project administration, T.V. ; funding acquisition, V.S.B. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable. Not applicable. Not applicable. Not applicable.