## 4 Numerical Study
### Analysis of Horizontal Deformation of Subway Tunnel  
Figure 11 is a cloud map of the horizontal deformation of the subway tunnel caused by the excavation of section A of the foundation pit under some working conditions. According to the simulation results of finite element software, as the excavation depth increases, the maximum horizontal deformation of the subway tunnel increases continuously. When excavating to the design elevation at the bottom of the foundation pit, the horizontal deformation of the subway tunnel reached 0.30 mm. With the removal of the reinforced concrete inner support of the foundation pit, the horizontal deformation of the subway tunnel has further increased. When all the inner supports are removed, the horizontal deformation has reached 0.49 mm. Figure 12 is a cloud map of the horizontal deformation of the subway tunnel caused by the excavation of section B of the foundation pit under some working conditions. The horizontal deformation trend of the subway tunnel caused by the  
Figure 10: Maximum vertical deformation of subway tunnel caused by foundation pit construction. exavation and the removal of the inner support in section B is similar to the construction of section A, which leads to an increase in the horizontal deformation of the subway tunnel. The horizontal deformation of the subway tunnel corresponds to the excavation of the foundation pit in section B, to the design elevation, and the removal of the first layer inner support is 0.42 and 0.62 mm, respectively. The maximum horizontal deformation of the subway tunnel caused by the construction of the foundation pit in section A and the foundation pit in section B is recorded in Table 5. In general, the horizontal deformation of the subway tunnel is smaller than the vertical displacement. The data in Table 5 are plotted as a line graph and recorded in Figure 13. It can be seen from Figure 13 that the variation trend of the simulated value of the maximum horizontal deformation caused by the construction in section A and section B is basically consistent with the monitored value. The monitoring value of the maximum horizontal deformation of the tunnel caused by the foundation pit construction is greater than the numerical simulation value, and the maximum horizontal deformation of the subway tunnel caused by the construction of the foundation pit section A is smaller than that of section B. The largest relative error in the construction process of the foundation pit section A appears in the first excavation condition, and its value is 33%. The largest relative error during the construction of the foundation pit section B also appears in the first excavation condition, and its value is 37.5%. The relative error of the numerical simulation is large, which is mainly caused by the small value of the maximum horizontal deformation of the subway tunnel itself. According to the code requirements of the area where the project is located, the horizontal displacement of subway structural facilities should be less than or equal to 10 mm. The maximum horizontal deformation of the actual subway tunnel caused by the construction of the foundation pit in section A and the foundation pit in section B is 0.49 and 0.62 mm, which are far less than the specification limit.