## 3 Results and Discussion
### Influencing Factors of Relatively Steady Seepage Field
#### 3.3.4 Influence of Evaporation  
When the effect of evaporation is considered, the rainfall subtracting evaporation capacity is taken as the flow boundary in the calculation model. Figure 13 shows the D-value between annual rainfall and evaporation capacity in Taiyuan, Zhengzhou, and Guiyang in 2020. The relative stable seepage fields considering evaporation effect were calculated, as shown in Figure 14.  
Figure 12: Distribution of the saturation line under different terrains of the tailings pond: (**a**) Taiyuan (annual rainfall of 400 mm); (**b**) Zhengzhou (annual rainfall of 800 mm); (**c**) Guiyang (annual rainfall of 1200 mm).  
Figure 13: Rainfall deducting evaporation in 2020.  
The minimum burial depth (\(h_{b}\)) of the phreatic line is defined as the minimum distance from the dam surface of the tailings dam to the phreatic line. As shown in Figure 14a, \(h_{b}\) is an important index for evaluating the safety of the seepage field of the tailings pond in Chinese specifications. Comparing Figures 11 and 14, when the evaporation time effect is considered, the changes of \(h_{b}\) under different working conditions are listed in Table 5.  
From Figure 6, when the annual rainfall was 400 mm, the maximum change of \(h_{b}\) increased from 23.9 m to 28 m, thus the increase ratio was 17.2%; when the annual rainfall was 800 mm, the maximum change of \(h_{b}\) increased from 19.4 m to 24.9 m, thus the increase ratio was 28.4%; when annual rainfall was 1200 mm, the maximum change of \(h_{b}\) increased from 15.2 m to 19.1 m, thus the increase ratio was 27.3%.  
Although the influence of evaporation is not considered in the rainfall seepage and stability analysis of most slopes [22; 23; 24; 25; 26], evaporation has a great impact on the seepage field of dry-stack tailings ponds under multi-year periodic rainfall conditions. Evaporation will reduce the water content of the tailings dam. Based on the above analysis in this paper, when considering the existence of evaporation, the RSSF will still be generated, whereas  
Figure 14: Saturation line of RSSF considering evaporation effect: (**a**) \(i=0.05\); (**b**) \(i=0.1\); (**c**) \(i=0.15\).  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Case**} & \multicolumn{3}{c}{**Annual Rainfall of 400 mm**} & \multicolumn{3}{c}{**Annual Rainfall of 800 mm**} & \multicolumn{3}{c}{**Annual Rainfall of 1200 mm**} \\ \cline{2-10}  & \(i=\) **0.05** & \(i=\) **0.1** & \(i=\) **0.15** & \(i=\) **0.05** & \(i=\) **0.1** & \(i=\) **0.15** & \(i=\) **0.05** & \(i=\) **0.1** & \(i=\) **0.15** \\ \hline Evaporation not considered & 23.9 & 23.4 & 23.2 & 19.4 & 19.2 & 19.1 & 15.8 & 15.3 & 15.2 \\ \hline Evaporation considered & 28.0 & 27.2 & 27.0 & 24.9 & 24.0 & 23.9 & 19.9 & 19.3 & 19.1 \\ \hline Difference rate (\%) & 17.2\% & 16.2\% & 16.4\% & 28.4\% & 25.0\% & 25.8\% & 25.9\% & 26.1\% & 27.3\% \\ \hline \hline \end{tabular}
\end{table}
Table 5: Minimum burial depth of the phreatic line (m).  
the distribution of the RSSF and the position of the saturation line will be reduced by the influence of evaporation. According to the above research results, if the influence of evaporation is not considered in the preliminary design of dry-stack tailings ponds, the design result will be safer. This may lead to further costs in the later construction of the tailings pond.