## 3 Simulation of the Influence of Shield Tunneling on Existing Subway Lines
### Analysis of Influence Numerical Simulation Results  
According to the above simulation scheme, the displacement of the Line 5 segment under different shield positions is obtained, as shown in Figure 5.  
Figure 4: Model meshing diagram (horizontal displacement constraints on the left and right sides, horizontal and vertical displacement constraints on the bottom). Figure 3: Schematic diagram of the model size in the intensely weathered section. As shown in Figure 5, when the horizontal center distance between the tunnels \(L_{2}\) is the same, the overall displacement trend of the Line 5 segment increases with the vertical center distance between the tunnels \(V_{2}\), and the displacement direction of the Line 5 segment gradually shifts to the lower right. Even if the vertical center distance between the tunnels \(V_{2}\) increases, the Line 5 segment is still in the range of stress disturbance caused by shield excavation due to the large diameter of the shield tunnel excavation. The missing stratum caused by shield excavation causes the redistribution of stress in the stratum. The soil near the segment tends to slide toward the inner part of the tunnel, and the sliding direction generally points to the center of the shield tunnel. As the vertical center distance between the tunnels \(V_{2}\) increases, the segment displacement direction gradually shifts downward and to the right. Figure 5 shows that, when the vertical center distance between the tunnels \(V_{2}\) is the same, with the increase in the horizontal center distance between the tunnels \(L_{2}\), the overall displacement trend of the Line 5 segment decreases. The position of the maximum displacement is basically unchanged, and the maximum displacement shows a decreasing trend. However, the displacement direction of the Line 5 segment does not change significantly. This indicates that with the increase in the horizontal center distance between the tunnels \(L_{2}\) (the shield tunnel moves to the right horizontally), the stress disturbance range formed by the shield excavation shifts to the right, and the influence on Line 5 is reduced. Moreover, the change in the horizontal center distance between the tunnels \(L_{2}\) does not cause a large deflection in the displacement direction of the segment, but the deflection in the displacement direction is highly sensitive to the change in the vertical center distance between the tunnels \(V_{2}\). As shown in Figure 6, with the increase in the vertical center distance between the tunnels \(V_{2}\), the maximum point of the displacement of the east line of Line 5 gradually moves upward, and the maximum displacement of the Line 5 segment shows an increasing trend. Thus, with the increase in the vertical center distance between the tunnels, the stress disturbance range caused by shield excavation shifts downward, and the influence effect  
Figure 5: Line 5 displacement change diagram. on the displacement disturbance range of Line 5 decreases. Therefore, the disturbance of the soil mass under the Line 5 segment decreases, and the influence factor of the maximum displacement point becomes the self-weight extrusion of the soil mass above the segment. Figure 7 shows the contour map of the change in the maximum displacement of the Line 5 segment with the change in the spatial relationship between Line 5 and the shield tunnel. The smaller the horizontal center distance between the tunnels \(L_{2}\) and the greater the vertical center distance between the tunnels \(V_{2}\), the greater the overall displacement of the Line 5 segment. The maximum value occurs at the lower left corner of \(L_{2}\) = 20 m, \(V_{2}\) = 16 m, and the displacement is 17.9 mm. The greater the horizontal center distance between the tunnels \(L_{2}\), the smaller the vertical center distance between the tunnels \(V_{2}\), and the smaller the displacement of the Line 5 segment. The minimum displacement appears in the upper right corner of \(L_{2}\) = 26 m, \(V_{2}\) = 8 m, and this displacement is only 2.8 mm.