## 2 Materials and Methods  
### Field Investigation  
The MSE wall under study was constructed in 2005 to secure a site on the backside and extends 211 m. A longitudinal crack deformed the corner height of the MSE wall by 14.1 m. The longitudinal crack-affected section was managed through displacement measurements. Figure 1 shows the construction plan and cross-sectional view of the MSE wall displacement section. An investigation was conducted to determine the cause of the longitudinal cracking at the MSE wall's corners. Drilling and electrical resistivity surveys were conducted on the MSE wall backfill and the underlying subgrade to distinguish between a straight section with no cracks and a corner with multiple longitudinal cracks. The straight section and corner were surveyed at STA.45 and STA.80, respectively, and the geotechnical survey was conducted at a depth of less than 1 m. 'STA(Station)' refers to a measurement word used to indicate a specific survey location on a drawing. Figure 2 presents the geotechnical survey plan, and Table 1 shows the geotechnical survey depths for each survey location. Figure 1: Field floor plan of MSE wall: (**a**) MSE wall construction plan view; (**b**) representative cross-section of MSE wall. Figure 2: Geotechnical survey locations. The results of the ground investigation confirmed that layers from TP-1 to TP-3 were reclaimed soil layers and TP-4 was a topsoil layer. The soil type of TP-1 and TP-2 sites were identified as silty sand with gravel, and TP-3 as clay with gravel. Moreover, the soil type of the TP-4 site comprised low-plasticity clay with sand. Table 2 shows the engineering properties of each investigated site. The electrical resistivity survey was conducted to determine the condition of the reinforced earth mass of the MSE wall. An electrical resistivity survey is a common non-destructive exploration technique used to determine the condition of the ground by measuring the potential difference caused by the difference in electrical resistivity among the differences in underground electrical properties. The electrical resistivity survey instrument supplies power to two current electrodes through an ammeter connected to a power source. It works on the principle that the potential difference is measured using an electrometer connected to two other potential electrodes through the supplied current. In this research, the electrode spacing of the electrical resistivity survey was installed at 5.0 m in order to consider the exploration depth and exploration extension of the ground. In addition, the ground condition was evaluated to identify leakage and problem areas distributed inside and around the MSE wall. The instrument used for the electrical resistivity survey is shown in Figure 3. \begin{table}
\begin{tabular}{c c c} \hline \multirow{2}{*}{**Separation**} & \multicolumn{2}{c}{**Depth of**} & \multirow{2}{*}{**Ground Layer**} & \multirow{2}{*}{**Remarks**} \\  & & **Investigation (m)** & & \\ \hline TP-1 & 0.0 to 0.8 & & Straight \\ TP-2 & 0.0 to 1.0 & Reclaimed soil layers & Corner (top) \\ TP-3 & 0.0 to 0.5 & & Corner (bottom) \\ TP-4 & 0.0 to 0.3 & & Topsoil layer & Original ground \\ \hline \end{tabular}
\end{table} 
Table 1: Geotechnical survey contents.