## 2 Design and Construction of the Full Scale RSR
### Design of RSR  
The ground conditions of the RSR construction site are shown in Figure 4. The ground consisted of 0.5 m thick fill, 0.5 m silty clay, 1.2 m silty sand, and 4.7 m weathered soil. To ensure the stability of circular failure, the fill layer was replaced with gravel up to a depth of 1.5 m. The backfill was constructed by dividing it into upper and lower subgrades of 3 m and 2 m, respectively, and materials that meet the Korean Railroad Design Standard were used. The soils used for the backfill were subjected to water content ratio, specific gravity, particle size distribution, shear, and compaction tests. The test results are presented in Table 2. Evaluation by the unified classification method, confirms that the backfill material used for the upper subgrade was gravelly soil (GP-GM), and for the lower subgrade, sandy soil (SP-SM). The material properties used for the stability analyses considering the results of the ground investigation and material tests are shown in Table 3.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Sections**} & **Vertical Spacing of Reinforcement (m)** & **Length of Short Reinforcement** & **Connection Types** & **Functions to Connect** \\ \hline
1L & 0.3 & 1.75 m (0.35 H) & Welding & Very Strong \\ \hline
1R & 0.3 & 1.50 m (0.3 H) & Hinge \& Bolt & Strong \\ \hline
2L & 0.4 & 2.00 m (0.4 H) & Welding & Very Strong \\ \hline
2R & 0.4 & 1.75 m (0.35 H) & Wind bold wire & Weak \\ \hline \hline \end{tabular}
\end{table}
Table 1: Detailed specifications of four sections.  
Figure 3: Cross sections of the full scale RSR.  
Each section was designed using the two-wedge method, which calculates the earth pressure acting on the wall and the minimum factor of safety from the equilibrium of the force [19]. The force acting on the two soil wedges is calculated while varying the angle of the two lines that form the failure surface in the backfill, as shown in Figure 5. Table 4 shows the safety factors of the circular failure, overturning, and sliding of each section. In all cases, it was confirmed that the safety factors satisfied the specifications of the Korean Railroad Network Authority [20]. The resisting moment is calculated by the multiplication of resistance and moment arm, so the narrower vertical spacing of the reinforcement increases the safety factors of overturning. In the cases of the reinforcement has short length (1R section) or wide vertical spacing (2L, 2R section), the safety factor of overturning tends to be smaller than sliding. However, in the 1L section where the reinforcement has sufficient length and narrow vertical spacing, the safety factor of overturning is larger than sliding.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Materials**} & **Unit Weight** & **Cohesion** & **Friction Angle** \\  & **(kN/m3)** & **(kN/m2)** & **(c)** \\ \hline Backfill & 19 & 0 & 30 \\ \hline Gravel & 22 & 0 & 37 \\ \hline Fill & 18 & 5 & 25 \\ \hline Weathered soil & 19 & 15 & 25 \\ \hline Reinforcement & \multicolumn{3}{c}{Geogrid, Design tensile strength = 60 kN/m} \\ \hline \hline \multirow{2}{*}{Elev. (m)} & Thic-kness (m) & Column & \multirow{2}{*}{Layer} & U & Standard Penetration Test \\  & & & S & \\  & (m) & Section & C & N & N blow \\  & & S & (blower cm) & 10 & 20 & 30 & 50 \\ \hline \(-\) 0.50 & 0.50 & Fill & GM & \multirow{2}{*}{7/30} & \multirow{2}{*}{7/30} & \multirow{2}{*}{7/30} \\ \(-\) 1.00 & 0.50 & Silty clay & CL & & 12/30 \\ \hline \multirow{4}{*}{\(-\) 2.20} & \multirow{4}{*}{1.20} & Silty & SM & \multirow{2}{*}{8/30} & \multirow{4}{*}{6/30} \\  & & & sand & & \\ \hline \end{tabular}
\end{table}
Table 3: Material properties for RSR design.  
Figure 4: Ground condition.