## 3 Three-Dimensional Numerical Model
### Finite Element Calculation Parameters
#### 3.2.3 Existing Tunnel Operational Loads
The maximum settlement value of the tunnel is 0.80 mm, and the maximum settlement of the track base plate is 0.63 mm. After S7 and S8 excavation, the tunnel and track surface settlement maximum values occur in the same location as S6, but the maximum settlement value points from the tunnel arch waist position to the bottom of the arch position move. The S7 excavation tunnel maximum settlement value of 1.23 mm, and the maximum settlement of the track base plate is 1.04 mm. The S8 excavation tunnel maximum settlement value is 1.85 mm, and the maximum settlement of the base plate is 1.66 mm. The maximum settlement value is 1.66 mm at both ends of the tunnel, and the settlement becomes smaller in a symmetrical trend. After S9-S12 excavation, the maximum settlement of the tunnel and track surface tends to coincide with the location of the maximum value, which occurs in the location of the tunnel floor, 120 m away from the A end. The tunnel-sensitive area occurs in the 120 m area on both sides of the maximum settlement value, and the A end area is larger than the B end area. The maximum settlement value of the tunnel after the excavation of S9 is 2.52 mm, and the maximum settlement of the track floor is 2.49 mm. The maximum settlement value of the tunnel after the excavation of S10 is 2.92 mm, and the track floor is 1.66 mm. The maximum value becomes smaller toward both ends of the tunnel. After S10 excavation, the maximum settlement of the tunnel is 2.92 mm, and the maximum settlement of the track base plate is 2.92 mm. After S11 excavation, the maximum settlement of the tunnel is 3.26 mm, and the maximum settlement of the track base plate is 3.24 mm. After S12 excavation, the maximum settlement of the tunnel is 3.59 mm, and the maximum settlement of the track base plate is 3.51 mm. The maximum value of the tunnel is the same as the tunnel at the two ends of the settlement law. The maximum settlement of the tunnel and track surface after the excavation of S13-S20 is 130 m away from the A end of the tunnel floor, and the increase in settlement value is small. Figure 12 shows the combined settlement curves of the track surface of the existing tunnel under different timing steps. In Figure 12, it can be seen that the maximum settlement of the track surface from S7 to S11 occurs to the right of the left line crossing point. This is because the excavation of the new tunnel is at an angle of 61\({}^{\circ}\) with the existing tunnel (as shown in Figure 6), and the left line is the first to be excavated and is three timing steps ahead of the right line, so the left line of the existing tunnel is the first to be affected by the excavation of the new tunnel. As the tunnel excavation progresses, the maximum settlement value gradually approaches the measurement point. At the end of the excavation, it can be observed that the settlement curve is symmetrically distributed based on the measurement points. In Figure 12, it can be clearly seen that the track surface settlement curve is characterized by significant features: the excavation area of S7\(\sim\)S14 is the sensitive area affected by the excavation of the new tunnel on the existing tunnel, and the settlement changes are large. The settlement of the new tunnel on the existing tunnel is concentrated in the strong disturbance area of 120 m at the measurement point, and the weak disturbance area is 60 m around the strong disturbance area.