## 5 Numerical Simulation Results
### The Lateral Displacement Analysis of Ground Surface  
In order to study the difference between the lateral displacement characteristics of the curved tunnel and the straight tunnel, a curved tunnel with a curved radius of 350 m and a straight tunnel were established, respectively, and the influence of the curved radius on the lateral displacement of the ground surface was studied. The lateral displacement of the surface soil after the excavation of the small radius curve and the straight tunnel is shown in Figure 8.  
It can be seen from Figure 8 that the lateral displacement of the soil on both sides of the conventional straight tunnel after shield excavation is roughly symmetrically distributed with the double-line center line of the tunnel as the axis, which is consistent with the research conclusions of some scholars [29; 30]. The lateral displacement of the soil on both sides of the tunnel with a small radius curve after shield excavation shows an obvious asymmetric shape with the double-line center line of the tunnel as the axis, and the lateral displacement of the soil on the inner side of the curve section is wider.  
Figure 7: Settlement curve of surface soil after double-track tunnel excavation.  
At the same time, in order to explore the influence of different curve radii on the lateral displacement of the ground, this paper selects four types of shield tunnels as the research objects, namely 100 m, 350 m, 600 m, and straight tunnels, and selects the line between the inner and outer centers of the surface of the curve model in Figure 2 as the monitoring line, and records the lateral displacement value of the surface here. The lateral displacement value of the ground surface at different tunnels is shown in Figure 9.  
It can be seen from Figure 9 that the lateral displacement curves of the ground surface after the excavation of tunnels with different curve radii are basically the same, that is, the lateral displacement of the ground surface on the outside of the curve section changes more obviously. The maximum lateral displacement of the curve radius with 100 m, 350 m, 600 m, and the straight tunnel is 7.40 mm, 6.77 mm, 6.50 mm, and 6.45 mm, respectively. Taking the lateral displacement corresponding to the straight tunnel as the benchmark, the  
Figure 8: Lateral displacement of surface soil after double-track tunnel excavation: (**a**) lateral displacement of surface soil in small radius curve tunnel; (**b**) lateral displacement of surface soil in straight tunnel.  
Figure 9: Lateral surface displacement curve after double-track excavation of a small radius curved tunnel.  
lateral displacement of the surface corresponding to the curve radius of 100 m, 350 m, and 600 m increased by 14.85%, 4.98%, and 0.88%, respectively. This is because when the radius of the curve is smaller, the more the stratum is over-excavated inside the curve section, the more intensified the stratum disturbance. It can also be found that the lateral displacement of the surface of the tunnel with the curve radius will move inward, and the soil body with lateral displacement on the inside is wider. The lateral displacement of the soil will cause a shear layer in the stratum and affect the structural stability of the shallow foundation building. Therefore, it is necessary to consider the reinforcement of the building on the inner side of the curve before the shield construction of the small radius curve tunnel.