## 4 Numerical Results and Discussion  
### Numerical Model Accuracy Verification  
In order to confirm that the established numerical model can effectively reflect the actual situation of the site and has certain guiding significance for the actual project, the validity of the established numerical model needs to be verified. The accuracy of the numerical model was verified by comparing the vertical settlement of the left tunnel vault monitoring point 40 m away from the portal with the excavation process and the final vertical settlement of the right main tunnel vault during the excavation of the main tunnel. In the numerical model and field monitoring, the vertical settlement curve of the vault of the left tunnel at the monitoring point 40 m away from the portal during tunnel excavation is shown in Figure 5. It can be seen from the figure that the shape of the vertical settlement curve of the vault at the same position of the numerical model and the field monitoring was similar, and the changing trend was the same. The vertical settlement of the vault of the left tunnel increased with the increase of the excavation depth. When the excavation depth of the left tunnel was 40-50 m, the vertical settlement of the vault increased rapidly, and the vertical deformation of the vault at this position shows a slowly increasing trend.  
Subsequently, after the completion of the tunnel excavation, the numerical calculation and field monitoring of the final vertical settlement of the vault of the right tunnel at different distances from the tunnel portal was compared and analyzed, as shown in Figure 6. It can be seen from the figure that at a certain distance from the portal, the simulation results were similar to the monitoring results, and the changing trend was the same. Within the range of 0-90 m from the portal, the vertical settlement of the vault was small. The farther away from the portal, the greater the vertical settlement of the vault. In the numerical calculation, the vertical settlement of the vault varied within 4.09 mm-24.76 mm, and in the field monitoring, the vertical displacement of the vault varied within 3.80 mm-23.3 mm. Comparing the simulated value with the monitored value, it can be found that the monitored value basically fluctuates up and down on both sides of the simulated value, and the two values were similar. In the range of 90-110 m from the portal, due to the existence of fault fracture zone here, the simulation value and monitoring value of vertical settlement of the vault were large, and showed a trend of first increasing and then decreasing. The maximum simulation value reached 30.67 mm and the maximum monitoring value reached 29.5 mm. In this area, there was little difference between the simulated value and the monitored value, and the changing trend was the same. Within the range of 110-140 m from the portal, with the increase of the distance from the portal, the vertical settlement of the vault gradually decreased, and the variation range of vertical displacement was  
Figure 5: Vertical settlement of left tunnel vault at 40 m away from the portal.  
12.07 mm-21.24 mm (simulated value) and 8.50 mm-14.80 mm (monitored value). The maximum error between the simulated value and the monitored value was 6.44 mm, the minimum error was 0.03 mm and the average error was 1.95 mm. In summary, the three-dimensional numerical model has a good simulation effect.