## 3 Results
### Construction of Numerical Model for Stability Analysis  
The DTM5 derived in 2003 before the 2005 event was used for construction of the model slope. The slope profile for stability analysis was vital for yielding proper results and was often taken as along the main sliding direction of the landslide. From the previous research of the Lantai deep-seated landslide, the main sliding direction was estimated as along the profile line X-X\({}^{\prime}\) shown in Figure 12[31]. Distribution of the ground layers at the site were determined referring to the borehole data of previous research [15; 16; 17; 18]. Four boreholes were drilled from 2015-2017 by [PERSON] et al. [15; 16; 17], and the borehole LTW04 located close to the profile X-X\({}^{\prime}\) was used. The borehole LTW05 located approximately along the profile X-X\({}^{\prime}\) was also used, which was drilled by [PERSON] et al. in 2018 [18]. Locations of both boreholes LTW04 and LTW05 were shown in Figure 12. [PERSON] inspected the borehole  
Figure 13: Photographs of out-crops in field: (**a**) out-crop A, (**b**) out-crop B with the moist black fault gouge material, (**c**) out-crop C also showing moist black fault gouge material, and (**d**) photo taken in October, 2015 after Typhoon Soudelor showing out-crop D with moist black material exposed. loggings and cores, and classified the ground layer distribution into three types of layer, i.e., the top soil, the shear zone, and slate [32]. By taking the profile along line X-X', the slope profile was constructed based on DTM5 as shown in Figure 14. Ground layer distribution of the two borehole loggings were presented in Figure 14, and the shear zone bounded by the geological structure surfaces was projected on the profile. It was found that location of the projected shear zone matched the distribution of shear zone material identified in the borehole loggings marked as red blocks in Figure 14. Samples of the shear zone material were taken and tested in the laboratory for the material property parameters by [PERSON] and [PERSON] [32; 33]. The material property parameters of the Lushan slate were obtained from previous research experiences and literatures [34; 35; 36]. The thickness of the top soil was small and had little effects on the failure mechanism of the deep-seated landslide compared to the main slope body, and thus was neglected in the numerical model analysis. Parameters of the material property used in the numerical model analysis are listed in Table 1. The Lantai landslide events were usually caused by heavy rainfall induced by typhoons, thus the ground water condition would play an important role for stability analysis. Due to lacking ground water monitoring data in field, location of the ground water table was assumed to follow the steady-state seepage when subjected to long-term precipitation, and was adjusted to consist with the water table record of the borehole LTW4. This ground water table is considered as reasonable but lower than the potential water table caused by the heavy rainfall event. The resulting numerical slope model with the ground layers and water table is as shown in Figure 15. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{\begin{tabular}{c} **Ground** \\ **Layer** \\ \end{tabular} } & \begin{tabular}{c} **Mass** \\ **Density** \\ **(kg/m\({}^{3}\))** \\ \end{tabular} & \begin{tabular}{c} **Bulk** \\ **Modulus** \\ **(GPa)** \\ \end{tabular} & \begin{tabular}{c} **Shear** \\ **Modulus** \\ **(GPa)** \\ \end{tabular} & \
\begin{tabular}{c} **Cohesion** \\ **(kPa)** \\ \end{tabular} &
\begin{tabular}{c} **Friction** \\ **Angle (\(\diamond\))** \\ \end{tabular} \\ \hline \hline slate & 2700 & 2.92 & 1.35 & 180 & 35 \\ shear zone & 2700 & 1.59 & 0.73 & 100 & 25 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Parameters of material property of each ground layer used in the numerical analysis.