## 4 Numerical Results and Discussion
### Stability Analysis of Large Section Tunnel under Different Excavation Sequences
#### 4.3.1 Deformation Analysis of Lining  
The displacement of the target section lining during the removal of the temporary support and secondary lining construction in two working conditions was analyzed. Figure 20 shows the vertical displacement of the lining after the removal of the temporary support, and Figure 21 shows the vertical displacement of the lining after the application of the secondary lining.  
Figures 20 and 21 illustrate that the different conditions of removing the temporary supports and applying the secondary lining have minimal influence on the overall vertical displacement of the lining but affect the distribution range and value of the maximum displacement on the upper part of the lining. The temporary support was layered removed in Condition 2 and overall removed in Condition 1. The distribution range of the maximum vertical displacement was small in Condition 2 because its construction was performed after the deformation of the primary lining tended to be stable. However, because of layered removal, the vault subsidence value of the disturbance to surrounding rock in Condition 2 was also bigger. In terms of the scope of the disturbance of surrounding rock, Condition 2 can be constructed after the primary lining deformation was relatively stable, and the disturbance range of the surrounding rock around the vault was small because Condition 2 had the layered demolition of the temporary support compared with the overall demolition form of Condition 1. However, due to the layered demolition, the settlement value at the vault under Condition 2 was also large.  
Figure 21: The vertical displacement of lining after the construction of the secondary lining (unit: m): (**a**) Condition 1 and (**b**) Condition 2.  
Figure 20: The vertical displacement of the lining after the temporary support was removed (unit: m): (**a**) Condition 1 and (**b**) Condition 2.  
Figure 22 shows the horizontal displacement of the lining after removing the temporary support and Figure 23 shows the horizontal displacement of the lining after the application of the secondary lining. Figure 22 shows that after removing the temporary support, the horizontal displacement of the tunnel changed significantly because of the overall removal of Condition 1, and the maximum horizontal displacement of the lining reached 0.9628 mm. After no vertical support was observed in the tunnel, the concentrated horizontal displacement to the surrounding rock side occurred on both sides of the arch waist. In Condition 2, the horizontal displacement was mainly concentrated on the lateral support, while the deformation at the arch was relatively stable, and the maximum horizontal displacement of the lining was 0.7695 mm. Figure 23 indicates that the horizontal displacement distribution of the overall lining in Condition 1 was improved after the application of the second lining, and the overall deformation of the lining structure was relatively uniform, with the maximum horizontal displacement being 0.7312 mm. The lining deformation in Condition 2 was less than that in Condition 1, and the maximum horizontal displacement of the lining in Condition 2 was 0.5546 mm.