## 4 Numerical Results and Discussion
### Analysis of Numerical Simulation Results of Main Tunnel Excavation
#### 4.3.3 Deformation Analysis of the Middle Partition Wall  
The middle partition wall was an important part of the supporting structure of the double-arch tunnel. The stress of this part was complex and changeable with the construction process. In the tunnel supporting structure, the deformation and stress of the middle partition wall cannot be ignored, and its structural stability was related to the overall stability of the double-arch tunnel supporting structure [32]. As the tunnel excavation created free faces on both sides of the middle partition wall, the risk of structural damage to the middle partition wall was greatly increased. Under the pressure of surrounding rock, the horizontal displacement of the middle partition wall was often too large, affecting the stress of the middle partition wall and even the overall support structure. Additionally, due to the different contact area, structural form and bearing pressure, the horizontal displacement of the top and bottom of the middle partition wall were often quite different, so the torsional deformation of the middle partition wall structure cannot be ignored. The measurement point A above the partition wall and the measurement point B on the  
Figure 17: Vertical deformation of vault lining during main tunnel excavation (unit: m): (a) L = 20 m; (b) L = 40 m; (c) L = 60 m; (d) L = 80 m; (e) L = 100 m; (f) L = 120 m; (g) L = 140 m; (h) Excavation of right tunnel to 130 m; (i) The main tunnel excavation is completed. abdomen were selected as the monitoring points for the horizontal deformation of the partition wall, as shown in Figure 19. The degree of torsional deformation of the partition wall was represented by the difference between the horizontal displacements of the top measurement point A and bottom measurement point B. Figure 20 shows the displacement of the middle partition wall at different sections after the main tunnel excavation. Figure 20a-g shows the tunnel cross-sections as Y = 20 m, 40 m, 60 m, 80 m, 100 m, 120 m and 140 m. The displacement values of the middle partition walls at the seven sections were different, and the directions were also different. The maximum displacement of the middle partition wall in seven sections was 1.59 mm, 1.71 mm, 2.25 mm, 6.51 mm, 6.24 mm, 2.73 mm and 1.83 mm, respectively. At the Y = 80 m and Y = 100 m sections, the displacement of the middle partition wall was relatively large. This was because the location was located in the fault fracture zone, the rock and soil was weak, the stability was poor, and the supporting structure was complicated. Therefore, the middle partition wall had a large deformation under the pressure of surrounding rock. On the Y = 20 m section, the vertical displacement of the middle partition wall was upward, indicating that under the reinforcement of rotary jet grouting pile, the surrounding rock strength of the portal section was high, the self-supporting capacity was strong, the surrounding rock pressure on the top of the middle partition wall was small, and the downward vertical displacement was not obvious. As the distance between the section and the portal increased, the direction of the vertical displacement of the partition wall gradually  
Figure 19: Deformation monitoring point of the middle partition wall. Figure 18: Vault settlement of the main tunnel. developed downward. The horizontal displacement direction of the middle partition wall at each section was the negative direction of the \(x\)-axis, that was, it moved towards the free face of the left tunnel (the main tunnel excavated first). Therefore, during the excavation of the main tunnel, the influence of the excavation sequence on the horizontal displacement of the middle partition wall was that the middle partition wall moved slightly towards the main tunnel excavated first. Therefore, during the excavation of the main tunnel, the influence of the excavation sequence on the horizontal displacement of the partition middle wall was that the partition middle wall moved slightly towards the main tunnel excavated first.