## 3 Field Test
### Monitoring Results  
The results of arch settlement monitoring for three sections, YK2 + 128, YK2 + 132, and Y2 + 134, are listed in Table 2. YK2 + 132 is selected as a typical section to analyze the spatial and temporal variation law of the arch settlement. The duration curve of each monitoring point is shown in Figure 7.  
As shown in Table 2, the highest settlement value for each section is found in the left drift (No.1 point). The maximum settlement value is 107.0 mm, which is less than the reserved deformation amount of 180.0 mm. This indicates that the initial support can control the tunnel deformation and eventually lead to a stable state. When comparing the settlement value in each drift, it is evident that the left drift experiences the largest settlement, followed by the middle drift, and finally the right drift. This observation is made in the context of the double-side drift method. \begin{table}
\begin{tabular}{c c c} \hline
**Position** & **Maximum Value/mm** & **Average/mm** \\ \hline Middle drift arch (0) & 46.4–54.5 & 51.0 \\ Left drift arch (1) & 76.7–107.0 & 87.0 \\ Right drift arch (2) & 19.0–5.97 & 40.7 \\ \hline \end{tabular}
\end{table} 
Table 2: Monitoring results of arch settlement. Figure 6: Layout of the initial supporting deformation test section. Figure 7: Arch settlement duration curve of YK 2 + 132. Figure 7 shows that the arch settlement undergoes three stages: rapid growth, slow deformation, and stabilization, and finally reaches a relatively stable state. The excavation of the right drift has led to a significant increase in the settlement rate of the left drift. Similarly, the excavation of the middle drift has resulted in a significant increase in the settlement rate of both the left and right drifts. These findings suggest that the excavation of the posterior drift has a significant impact on the structural stability of the drift. During the period between the excavation of each drift and the removal of temporary support, the average settlement rate of the left drift was 0.84 mm/d, while the average settlement rate of the right drift was 0.49. The settlement rate of the middle drift reached 1.11 mm/d, the highest among all drifts. This indicates that the arch settlement rate of the middle drift is higher than that of the other drifts, resulting in a greater final settlement compared to the right drift excavated first. The left drift, which is located on the deep buried side, experienced the longest deformation time and the most disturbances, resulting in the greatest final settlement among all drifts. After the temporary support was removed, the arch of the drift experienced short-term and rapid settlement, followed by a gradual stabilization. This indicates that the stress in the arch structure was distributed at this time, and the slow deformation of the middle drift was also halted, resulting in the gradual stabilization of the arch structure. The results of convergence monitoring for three sections, YK2 + 128, YK2 + 132, and Y2 + 134, are listed in Table 3. YK2 + 132 is selected to analyze the law of convergence. The duration curve of each monitoring point is shown in Figure 8.  
As shown in Table 3, the highest convergence value for each section is found in the left drift (5-5\({}^{\prime}\)). The maximum convergence value is 108.8 mm. and this value is less than the reserved deformation amount of 180.0 mm, indicating that the initial support can control the tunnel deformation and eventually lead to a stable state. When comparing  
Figure 8: Convergence duration curve of YK2 + 132.