## 5 Results
The results demonstrated that the different shear parameters affected the size of the sliding body and much more the calculated factor of safety. Figure 12a shows that the potential sliding surface occurred only at the toe position of the slope without seepage, regardless of whether the mean or the 5% fractile or 95% fractile values were taken. The values of the cohesion and friction angle were very different between these three sets of shear parameters, and the effect on the position of the calculated slip shear zone and on the factor of safety was large. The FoS for the 5% strength fractile was less than one, which indicated that the slope would fail at the toe in its current geometry without further triggering, which did not fit the observations. This suggests that the engineering practice of taking a 5% fractile as a cautious estimate for strength parameters is appropriate for engineering purposes but may not be well suited for natural hazard prediction. For the case of a high groundwater level (GWT3-1458 m), there were some differences in the location of the upper scarp of the landslide obtained with the three sets of strength parameters, but they had little effect on reflecting the overall sliding trend of the upper glacial deposits layer. More importantly, all results were close to the assumed shear zone from the geological investigation. The FoS for the 95% strength fractile was slightly larger than one. This indicated a situation that was very close to the limit state and could be interpreted as highly vulnerable to failure, compared to the FoS of 1.3 normally required by engineers to ensure a long-term stable situation of geotechnical structures. In general, the results obtained with the mean strength parameters were plausible, and the main mechanical difference between no seepage and high groundwater level was reflected by all three parameter sets. However, a prefailure analysis as a so-called class A prediction [83] would require more samples to reduce the scatter in the determination  
Figure 11: Safety analysis with the initial groundwater table at 1458 m: (**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). of strength parameters. Nonetheless, the following analyses of pore pressure distribution and influence of permeability were conducted with the mean strength parameters as the qualitative influence was expected to be the same for all three parameter sets. The pore pressure distribution at the location of the basal shear zone (marked by the red dashed line in Figure 7a) with different groundwater levels is shown in Figure 13. During the process of the initial groundwater level being raised by tens of meters (the average groundwater level rise in the slope was around 36 m) from GWT1 to GWT3, the maximum value of the pore pressure at the basal shear zone increased from a few tens of kilopascals to around 400 kPa. The increase of the pore pressure reduced the effective stresses and led in combination with the seepage force to the instability of the slope. The different computation methods revealed very similar results in pore water distribution.