## 4 Comparison between the Monitoring Data and the Results of 3D FEM Analysis
### Comparison with the Monitoring Data of an Inclinometer  
In this study, an inclinometer (SID) was installed in conjunction with the construction of the retaining piles to measure the lateral displacement of the ground and the retaining piles after excavation. There were three inclination instruments (numbered SID-01, SID-02, and SID-03 respectively) buried in the south area of this case, and the buried depth of the retaining piles was 9.25 m. Table 3 shows the data observed for the maximum displacement measured by the inclinometer (SID) in each construction stage in the south area. From the observation data in the table, it can be seen that the maximum value measured by the inclinometer appeared during the pouring of the concrete for the base plate in the south area. The maximum value was 1.07 mm and did not exceed the warning value (45 mm). It was observed that the retaining wall's structure was safe and stable during the monitoring period.  
A comparison between the results of the 3D finite element analysis and the monitoring data of an inclinometer (SID-002) is shown in Figure 15. For the subsidence results perpendicular to the direction of the railway track (the CD direction in Figure 15a), in the first stage of excavation, the maximum displacement of the ground in the numerical analysis was 0.2 mm, and the maximum subsidence of the monitoring data was 0.28 mm. In addition, in the second stage of excavation, the computational and monitoring values were 0.42 and 0.55 mm, respectively. Moreover, for the results of the analysis along the embedment direction of the retaining piles (the EF direction in Figure 15b), in the first stage of excavation, the maximum displacement of the retaining pile in the numerical analysis was 0.28 mm, and the maximum displacement in the monitoring data (SID-002) was  
Figure 14: Comparison of 3D FEM analysis results with the monitoring data on railway track subsidence (SR) for the total displacement of the excavation in stages 1 and 2: (a) along the AB direction; (b) along the CD direction.  
\begin{table}
\begin{tabular}{l c c c} \hline \hline \multirow{2}{*}{**Construction Stage**} & **SID-001** & **SID-002** & **SID-003** \\  & **(mm)** & **(mm)** & **(mm)** \\ \hline Assembly of the tie-beam formwork for & & & \\ retaining piles in the central area and & 0.17 & 0.42 & 0.42 \\ construction of steel piles in the south area & & & \\ Pre-stressed ground anchors for retaining piles & 0.67 & 0.50 & 0.70 \\ Pre-stressed ground anchors for steel piles & 0.76 & 0.54 & 0.81 \\ Pouring of concrete for the base plate in the south area & 1.07 & 0.57 & 0.91 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Maximum displacement measured by the inclinometers (SID) in each construction stage in the south area.  
0.29 mm. In addition, in the second stage of excavation, the computational and monitoring values were 0.93 and 0.95 mm, respectively. It could be seen that the computational values from the 3D finite element analysis and the monitoring values showed a very consistent distribution trend.  
The gravel layer in the construction area of this study not only had good self-support and a high shear strength, but it also had a gravel content of at least 75%. Under the condition of considering the live load of trains running on the railway and protecting the ballast of the track bed adjacent to the railway track, a temporary vertical wall with a depth of 4 m was added to the design as an early retaining wall measure, and it was connected with the subsequent construction of the retaining piles to increase the confinement capabilities. Therefore, the results of the comparison of the monitoring data and 3D finite element analysis showed that the displacement of the retaining wall was within a safe range and was stable.