## 5 Comparative Analysis of Monitoring Results and Numerical Results
### Monitoring and Analysis  
Firstly, it is necessary to clarify that relevant monitoring equipment was installed to observe the variation in the tunnel's stress and deformation along the entire tunnel, instead of limiting it to the ZK2985+360 section. Secondly, the geological survey report and field investigation show that there is a fault fracture zone (i.e., the most dangerous position along the tunnel) in the ZK2985+360 section. The monitoring results are displayed in Figure 12. This figure reveals that the maximum stress in the surrounding rock occurs at the location of the left arch foot. Notably, the actual monitored displacements are significantly larger than those predicted by numerical simulations. This discrepancy is primarily due to the fact that support structures in the numerical model are assumed to be applied instantaneously, whereas in the actual construction process, the application of support occurs with a relative delay. Additionally, the support materials require a certain period to undergo condensation and develop sufficient strength. Consequently, the measured displacements exceed those projected by the simulation [44]. To address this discrepancy, further exploration into the differences between the measured displacements and those predicted by simulations is necessary. Enhancing the model by incorporating actual construction conditions could improve \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Instrument Name** & \begin{tabular}{c} **Instrumentation** \\ **Management Number** \\ \end{tabular} & **Quantities** & **Note** \\ \hline Displacement meter & JK-QS003 & 20 & \begin{tabular}{c} Monitoring the internal displacement of the \\ surrounding rock \\ \end{tabular} \\ Steel rebar meter & JK-QS001 & 10 & \begin{tabular}{c} Monitoring of anchor shaft force \\ Monitoring of perimeter rock pressure and \\ Intersport pressure \\ \end{tabular} \\ Earth pressure cell & JK-QS004 & 40 & \begin{tabular}{c} Monitoring of internal forces in steel supports \\ \end{tabular} \\ Surface Strain Gauge & JK-QS005 & 40 & \
\begin{tabular}{c} Monitoring of internal forces in steel supports \\ \end{tabular} \\ Embedded Strain Gauge & FS-NM30 & 40 &
\begin{tabular}{c} Monitoring of internal lining stresses \\ \end{tabular} \\ Handheld vibrating string collector & FS-FP01 & 1 & Collection of monitoring data \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Monitoring instrumentation program. Figure 11: Measurement point arrangement and instrument location. its accuracy. To address the observed discrepancies between actual measured displacements and numerical simulations, further exploration and adjustment of the model in accordance with actual construction conditions are necessary. One potential modification could involve introducing a time delay factor for support construction within the numerical simulation. Additionally, more accurate modeling of the support's consolidation process could enhance the precision of the simulations. Implementing these changes would improve the accuracy of numerical models, allowing them to more effectively reflect the real-world engineering conditions. This approach not only aids in predicting potential issues but also assists in developing strategies to mitigate them during the construction phase. According to observations in Figure 12, during the excavation sequence, the minimum principal stress value was noted in the surrounding rock and initial support at the right arch waist location, aligning with the results from the numerical simulations. The tunnel section from ZK2985+195 to ZK2985+555 was selected as a comparison section, and the double-side drift method was used for excavation and support, in line with the actual construction conditions on site. The numerical model was adjusted by setting appropriate analysis steps to simulate the actual excavation conditions. To verify the accuracy of the model, we have compared the numerical results with the monitoring results, as illustrated in Figure 13a.