## 5 Numerical Model Establishment and Results Analysis
### Ventilation Shift Deformation Analysis  
Three indicators, namely the ventilation shaft deformation, the principal stresses of the surrounding rock, and the existing state of the surrounding rock, were analyzed to study the mechanical characteristics of the surrounding rock at the junction of the full-section excavation and TBM pilot tunnel excavation. The actual construction involves a daily advance of 4 m, corresponding to each construction step in the numerical simulation. (1) Vertical Displacement of the Arch Top  
The settlement data of the arch top at the end of each construction step for the analysis section were extracted to obtain the ventilation tunnel's arch settlement curve (Figure 9) and settlement table (Table 5). In Figure 9, the dashed line represents the beginning of a construction step. Taking the leftmost dashed line in Figure 9 as an example (denoted as S21 for the 21 st excavation step), it represents the last excavation segment of the full-section construction. From Figure 9 and Table 5, it can be observed that the arch top settlement at the analysis section underwent five stages: initial settlement, accelerated deformation, slow deformation, abrupt deformation, and slow growth. Before the completion of the full-section excavation (before S21), the analysis section was influenced by the excavation of other parts of the surrounding rock, resulting in some initial settlement. However, due  
Figure 8: Schematic diagram of the corrected rock parameters. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Construction Phase** & **Initial Settlement** & **Completion of Full Face Excavation** & **Completion of Full Face Support** & **Completion of TBM Tunnel Excavation** & **Excavation Expansion Begins** \\ \hline Settlement amount. (mm) & 0.81 & 4.19 & 4.22 & 6.21 & 10.2 \\ Final settlement. (mm) & & & 11.73 & & \\ Settlement ratio. & 6.91\% & 28.82\% & 0.26\% & 16.97\% & 34.02\% \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Table of vault settlements. Figure 9: Curve of crown settlement. to the distance between the excavation face and the analysis section (4 m and 16 m for the full-section excavation face and TBM pilot tunnel excavation face, respectively), the impact on the analysis section was limited, and the arch top settlement was only 0.81 mm, accounting for 6.91% of the total settlement. As the full-section excavation concluded (S21), the face became closer to the analysis section, and this construction segment was not supported after the excavation. Consequently, the arch top settlement experienced the first significant jump, reaching 4.19 mm. This stage accounted for 28.82% of the total settlement, indicating that the surrounding rock was in a state of accelerated deformation. When the full-section support was completed (S22), the TBM face continued to advance. At this point, the face was 8 m away from the analysis section, and the influence of the support at the full-section excavation on the surrounding rock at the TBM pilot tunnel excavation was limited. This resulted in a very small arch top settlement during this construction phase, with a final settlement of 4.22 mm, representing only 0.26% of the total settlement. The surrounding rock was in a state of slow deformation. When the TBM pilot tunnel excavation was completed (S24), the face reached the location of the analysis section. At this time, the arch top settlement increased to 6.21 mm, accounting for 16.97% of the total settlement. As excavation commenced (S25), the surrounding rock lost its constraint on the rock mass within the ventilation tunnel cross-section, leading to a rapid increase in deformation. The settlement reached 10.2 mm, accounting for 34.02% of the total settlement. The cumulative settlement at the end of the pilot tunnel excavation and the beginning of the enlargement accounted for 50.98% of the overall settlement, indicating that the surrounding rock was in a state of abrupt deformation.