## 4 Numerical Simulation Results Analysis
### Influence of Overburden Depth of Underpass on Surface Subsidence and Culvert Deformation  
In this section, having assumed that the soil parameters and box culvert parameters remained unchanged, the impacts of the shallow-buried pipe-roof box culvert on the surface subsidence and culvert deformation were examined for different overburden depths above the pedestrian underpass. Therefore, although the actual overburden depth of the underpass in the original project was 2.7 m, three other different overburden depths (i.e., 0.7, 1.7, and 3.7 m) were used to compare their effects on the surface subsidence and culvert deformation. The selected analysis points were a point on the ground above the symmetry axis of the box culvert, and points on the top and bottom of the box culvert, as shown in Figure 33.  
Figure 31: Bending moment distribution of the pipe-roof structure with an aspect ratio of 0.40. Figure 33: Schematic diagram of the locations of the analysis points. Under different soil depths, the analysis values for the vertical displacement of the G1 analysis point in each stage are shown in Figure 34. It can be seen from Figure 34 that when the launching and receiving shafts were completed, the surface subsidence of the observation point was about 10 mm. Later, the surface subsidence increased to about 14 mm due to the removal of the lateral supports. During the box culvert excavation stage, the shallow box culvert was affected by the buoyancy of groundwater. With the excavation of the box culvert, the overall weight of the box culvert decreased, and the amount of surface subsidence tended to decrease. Among the different soil depths, when the overburden depth was 3.7 m, the impact was the greatest, and when the overburden depth was 0.7 m, it was the least affected. In the steel sheet pile removal stage, the support of the steel sheet pile was lost under the top pipe roof, and the amount of surface subsidence at this stage tended to increase. The subsidence amount was the largest when the overburden depth was 0.7 m, and the subsidence amount was the smallest when the overburden depth was 3.7 m. According to the results, it was inferred that the shallow-burden box culvert was more sensitive to the subsidence caused by construction than the deep-burden box culvert. Nevertheless, the analysis results showed that for the shallow-burden depth underground passage, the effect of pipe-roof structure on the reduction of excavation face load is significant. This showed that the pipe-roof structure was suitable for underground excavation with shallow-buried depth in soft soil. This is consistent with the results of [PERSON] et al. [23]. After the excavation of the earthwork, the closed structure of the box culvert deformed under the action of external loads [5]. The deformations of the top and bottom of the box culvert are important indicators of the safety of the underground passage and ground buildings. According to the test results of [PERSON] and [PERSON] [14], the surface subsidence caused by the PPM during tunnel excavation was maximum at the position closest to the tunnel excavation face. Therefore, in this study, the center line of the box culvert roof 10 cm away from the excavation face of the box culvert was taken as the T1 analysis point, and the center line of the bottom plate 10 cm away from the excavation face was taken as the B1 analysis point to observe the vertical displacements of the top and bottom of the box culvert. The deformed height of the center of the box culvert was calculated by the displacements of these two points, and then the vertical deformation rates of the center of the box culvert were obtained by dividing the obtained height by the original height of the box culvert. Under different overburden depths, the analysis values of the vertical displacements of the T1 and B1 analysis points in each stage are shown in Figures 35 and 36, respectively.