## 5 Results  
Vertical slices were used in the LEA, and the results were obtained with the Spencer method. In the limit equilibrium model for the steady-state groundwater analysis, the approximate number of elements was 6000, and the element type was chosen as three-node triangles. In the finite element model, the number of elements approached 6000 and the mesh discretization was performed with 15-node triangular elements. Cases with FoS < 1 were computed with doubled starting strength parameters. The final safety factor was obtained by dividing the resulting value by a factor of two. In the finite element limit analysis, the strength-reduction method was used for the lower- and upper-bound calculations. In the computational model for the finite element limit analysis, the number of start elements was set as 6000 with mesh adaptivity. Very dense meshes were adopted for the area surrounding the assumed basal shear zone in the computational models with the strength-reduction finite element analysis and finite element limit analysis. It was computationally verified by a convergence study that the grid density settings in the models used in the three methods could obtain comparatively reliable results without excessive consumption of computational time. Figure 10 shows the mesh discretization and failure mechanisms without considering seepage obtained by the three methods, in which (a), (b), (c), and (d) correspond to the results of the limit equilibrium analysis, strength-reduction finite element analysis, and the lower and upper bound of the finite element limit analysis, respectively. It can be seen that the location of the shear zone occurred at the toe of the slope when seepage was not considered (FoS > 1). The calculation results for the groundwater table at its highest position are provided here as an example in Figure 11. At the left boundary of the computational model, the groundwater table was set at a fixed height that did not exceed the leftmost altitude, which was 1458 m. Figure 11 indicates that the slope was in an unstable state with its safety factor close to or less than one for this high groundwater level. The sliding surface appeared  
Figure 10: Safety analysis without the consideration of seepage: (**a**) sliding surface obtained with the LEA; (**b**) incremental shear strains obtained with the SRFEA; (**c**) shear dissipation distribution obtained with FELA (lower bound); (**d**) shear dissipation distribution obtained with the FELA (upper bound). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Initial Groundwater Table**} & \multirow{2}{*}{**LEA**} & \multirow{2}{*}{**SRFEA**} & \multicolumn{3}{c}{**FELA**} \\ \cline{3-6}  & & & **LB** & **UB** & **(LB + UB)/2** \\ \hline
0 & 1.30 & 1.37 & 1.37 & 1.39 & 1.38 \\ GWT1-1400 m & 1.19 & 1.27 & 1.33 & 1.35 & 1.34 \\ GWT2-1430 m & 1.10 & 1.16 & 1.23 & 1.24 & 1.24 \\ GWT3-1458 m & 0.93 & 0.94 & 1.00 & 1.01 & 1.01 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: FoS values obtained with different groundwater levels (LB: lower bound; UB: upper bound). mainly at the boundary of both layers in the calculation. The sliding area was quite large, starting from the upper middle of the slope, almost through the entire upper soil layer. The safety factors obtained by the three methods under no-seepage and seepage conditions are listed in Table 8. The FoS values indicated that the safety factor gradually decreased with the rise in groundwater levels until the slope became unstable. Figures 10 and 11 and Table 8 show how similar the FoS values and the failure mechanisms obtained with the three methods were. The calculation results obtained with the limits of the Mohr-Coulomb shear parameters as a 5% fractile and a 95% fractile under no-seepage and seepage (the initial groundwater table at GWT3-1458 m) conditions, are listed in Table 9 and shown in Figure 12. Only the results of the calculated sliding surface by the limit equilibrium analysis are shown here since the locations obtained by the two other methods were similar.