# Research on the Settlement Patterns of Tunnel-Surrounding Rock Under Groundwater Conditions
## 4 Results and Discussion  
### Settlement Monitoring Analysis  
Field monitoring data were collected and analyzed to generate comparative curves illustrating the settlements of the tunnel vault and the ground surface across various cross-sections.  
As illustrated in Figure 7, the ground surface and vault settlement curves for the five monitoring cross-sections initially decline rapidly, then decline gradually, and ultimately stabilize once the excavation distance reaches 35 m. This trend is primarily attributed to stress redistribution within the soil mass. During early excavation stages, soil stress is rapidly released, resulting in a high settlement rate. As excavation progresses, stress gradually transfers to the surrounding soil, establishing a new equilibrium and decreasing the settlement rate. Furthermore, as the excavation face moves away from the monitoring cross-sections, the disturbance zone decreases, and the soil strengthens through consolidation and compaction, naturally slowing the settlement rate. Consequently, groundwater conditions significantly affect both settlement and the time needed to reach a stable state.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Cross-Section**} & \multicolumn{3}{c}{**Vault Settlement (mm)**} & \multicolumn{3}{c}{**Surface Settlement (mm)**} \\ \cline{2-7}  & **Monitored** & **Simulated** & **Error Rate** & **Monitored** & **Simulated** & **Error Rate** \\ \hline Y = 40 m (Target 1) & 25.24 & 25.5 & 1.03\% & 9.23 & 9.73 & 5.42\% \\ Y = 45 m (Target 2) & 25.71 & 25.8 & 0.35\% & 10.38 & 10.87 & 4.72\% \\ Y = 50 m (Target 3) & 25.73 & 25.83 & 0.39\% & 11.54 & 11.94 & 3.47\% \\ Y = 55 m (Target 4) & 25.19 & 25.91 & 2.86\% & 12.23 & 12.9 & 5.48\% \\ Y = 60 m (Target 5) & 25.66 & 25.96 & 1.17\% & 13.24 & 13.8 & 4.23\% \\ \hline \hline \end{tabular}
\end{table}
Table 2: Comparison of simulated and monitored settlements at various monitoring cross-sections.  
Figure 6: Groundwater level diagram.  
If the water level rises, the effective soil stress decreases, accelerating plastic deformation and increasing the initial settlement rate, causing the stabilization point to occur earlier (e.g., at 30 m). Conversely, if the groundwater level drops, the soil skeleton strengthens, delaying plastic deformation development and pushing the stabilization point further (e.g., at 40 m) [41].  
The vault settlement rates and values are significantly higher than those of the ground surface, and the difference in settlements increases gradually with excavation progress. Monitoring data indicate that the maximum ground surface settlements for Targets 1 to 5 are 9.23 mm, 10.38 mm, 11.54 mm, 12.23 mm, and 13.24 mm, respectively, while the maximum vault settlements are 25.24 mm, 25.71 mm, 25.73 mm, 25.19 mm, and 25.66 mm, respectively. The settlement differences increase gradually during excavation, reaching maximum values of 16.01 mm, 13.33 mm, 13.19 mm, 12.56 mm, and 14.42 mm. Both ground surface and vault settlements tend to stabilize once excavation reaches 35 m.  
Figure 7: Comparison curves of vault and ground surface settlement in various monitoring cross-sections; (**a**) Target 1; (**b**) Target 2; (**c**) Target 3; (**d**) Target 4; (**e**) Target 5.