## 4 Results and Discussion
### Analysis of Excavation Methods
#### 4.2.2 Deformation Analysis  
(1) Deformation analysis of the surrounding rock and tunnel  
The vertical displacement of the tunnel under the two excavation methods is shown in Figure 17. In both excavation methods, the \"collapsed arch\" phenomenon was observed in the surrounding rock above the tunnel. For both excavation methods, the maximum vertical settlement of the tunnel occurred at the left side of the arch top of Tunnel 4. To further study the deformation process of the tunnel under both excavation methods, the vertical displacement at this point was plotted as a graph during the excavation process, as shown in Figure 18. It was found that, when the Three-bench Excavation Method was used, the settlement of the tunnel produced a larger increase in the upper-step construction stage. When the Center Diaphragm Excavation Method was used, the settlement produced a larger growth in the upper-step construction stage of the main cavern. Compared with the Three-bench Excavation Method, the deformation process of the tunnel was smoother when the Center Diaphragm Excavation Method was adopted. This was because the Center Diaphragm Excavation Method had a smaller excavation area and was equipped with temporary support. The final settlement when using the Center Diaphragm Excavation Method was 1.33 cm, while the final settlement when using the Three-bench Excavation Method was 1.48 cm. The Center Diaphragm Excavation Method was therefore slightly better than the Three-bench Excavation Method. The settlement of both excavation methods was within a safe range.  
Figure 17: Vertical deformation clouds under different excavation methods: (**a**) Center Diaphragm Excavation Method; (**b**) Three-bench Excavation Method.  
Figure 18: Deformation curve of vertical displacement of measurement points with excavation steps.  
(2)  
Tipping analysis of the middle partition wall  
The horizontal displacement of the middle partition wall under different excavation methods is shown in Figure 19. The middle partition walls under the two excavation methods were mainly deformed by tipping, and the maximum horizontal deformation occurred at the top of the middle partition wall on the shallow-buried side. The horizontal deformation of the top of the shallowly buried side of the middle partition wall under the two excavation methods was plotted in Figure 20. Regardless of the excavation method, the horizontal deformation at the top of the middle partition wall gradually increased during the construction process. Numerically, the final cumulative horizontal deformation of the diaphragm wall during excavation when using the Center Diaphrag Excavation Method and Three-bench Excavation Method was 2.85 mm and 3.79 mm, respectively. The Center Diaphrag Excavation Method was therefore slightly better than the Three-bench Excavation Method. However, it should be noted that the deformation of the middle partition wall under both excavation methods did not exceed 4 mm. Both were in a safe condition.  
Figure 19: Horizontal deformation clouds of the middle partition wall under different excavation methods: (**a**) Center Diaphrag Excavation Method; (**b**) Three-bench Excavation Method.  
Figure 20: Horizontal deformation clouds of the middle partition wall on the shallowly buried side under different excavation methods.