## 4 Numerical Results and Discussion
### Stability Analysis of Large Section Tunnel under Different Excavation Sequences
#### 4.1.2. Lining Deformation Analysis  
The analysis of the deformation of the lining in the tunnel structure was helpful in judging the unfavorable section in the construction process and in helping control the deformation of the surrounding rock. Figure 7 shows the vertical displacement of the primary support and temporary support in different conditions after penetrating the tunnel. As shown in the vertical displacement distribution of the primary support in Figure 7, in the three conditions, the maximum vertical displacement was distributed in the upper area of the primary support, which was 2.007, 2.201, and 2.259 cm, respectively. The minimum vertical displacement was distributed in the lower area of the primary support, which was 0.775, 0.727, and 0.809 cm, respectively. The temporary support carried the load from the upper part of the primary support to the lower part, thereby forming a closed loop inside the section. The vertical displacement was moderate, and the maximum value was 1.765, 1.825, and 1.986 cm, respectively. In terms of the maximum vertical displacement on the upper part of the primary lining, the larger displacement was most widely distributed in Condition 2, and Condition 1 was similar to Condition 3. The lateral displacement of temporary support was small because of the constraint at the portal. Figure 8 shows the vertical settlement variation curves of the vault at the target section in different calculation steps, and, similar to the vertical displacement of the ground surface, the vertical settlement of the tunnel vault also has a rapid development stage. Condition 1 lasted 11 calculation steps from 19 to 30, accounting for 23.9% of the total calculation steps. Condition 2 lasted 20 calculation steps from 10 to 30, accounting for 46.5% of the  
Figure 6: The variation curve of vertical surface displacement of the target section with calculation steps. Figure 7: The vertical displacement of the primary support and temporary support in different conditions (unit: m): (**a**) Condition 1; (**b**) Condition 2; and (**c**) Condition 3.  
total calculation steps, and Condition 3 lasted 22 calculation steps from 6 to 28, accounting for 61.1% of the total calculation steps. The end time of the rapid settlement stage was close, but the duration of this section was different in various construction conditions. In the whole excavation process of the tunnel, that is, from the perspective of the time control of vault displacement, Condition 1\(<\) Condition 2\(<\) Condition 3. In the three asynchronous sequences, the vertical displacement of the vault tended to be the same after tunneling, reaching 6.3 cm. During excavation, the horizontal displacement of the arch waist was also an important factor that affected the stability of the tunnel section. The arch waist of the right and left pilot tunnels of the target section were selected as the measuring points to analyze the horizontal displacement of the arch waist, as shown in Figure 9.  
Figure 10 shows the curve of the horizontal displacement of the measuring points in each working condition as construction progresses. In Conditions 1 and 2, the right pilot tunnel was excavated first, and the lateral displacement of the arch waist tended to the surrounding rock (Figure 10a,b). In Condition 3, the horizontal displacement tended toward the inside of the tunnel at the arch waist because of the influence of the middle pilot tunnel excavation. In the previous calculation steps, a sudden change occurred in the displacement curve of the measuring point. The increasing displacement was caused by the excavation of the rock mass part close to the target measuring points, and the reduction in displacement was due to the completion of the primary lining support.