## 4 Numerical Simulation of the Displacement Field
### Analysis of Horizontal Displacement of the Enclosure Structure  
During foundation excavation, soil change is a dynamic equilibrium process. When the soil body is unloaded, in order to reach a new balance, it will move from the position with high stress pressure to the position with low stress pressure. The soil bodies at different depth have distinct stress states and deformation. With the increase of excavation degree, the water pressure inside and outside the pit increases, and the seepage force generated by the groundwater infiltration increases. Therefore, in the process of excavation, the enclosure structure is deformed and moves sideways under the influence of soil and groundwater seepage force around the pit.  
It can be seen from Figure 18 that the maximum horizontal displacement of the enclosure structure is increasing during the construction of the foundation pit, and the maximum value is 3.8 mm in the first excavation, 7.4 mm in the second excavation, 13.8 mm in the fourth excavation, 23.5 mm in the fourth excavation, 41.2 mm in the fifth excavation, and 53.3 mm in the sixth excavation. The horizontal displacement of the enclosure structure was not obvious in the first excavation, and the maximum horizontal displacement of the enclosure structure increased significantly with excavation times. The location of maximum deformation gradually moved down with the excavation. After the excavation was completed, the maximum horizontal deformation was located at about 0.9 times the depth of the pit, near the bottom of the pit.  
From Figures 19-22, it can be seen that there are differences in the values of horizontal displacement of the enclosure structure with and without a leakage point in the construction process of the foundation pit. The maximum horizontal displacements of the enclosure structure are 36.1 mm, 39.1 mm, and 43.5 mm when the leakage point is 0.01 m wide, 0.005 m wide, and 0.001 m wide, respectively, and the maximum horizontal displacement was 53.3 mm when there is no leakage point. The overall deformation trend is consistent, and the curves are bell-shaped with small values at both ends and large values in the middle.  
The leakage of the enclosure structure does not change the form of horizontal displacement of the enclosure structure, and the displacement of the enclosure structure gradually decreases as the leakage defect increases This is due to the total pressure reduction at the outer wall-soil interface of the enclosure structure. In other words, this phenomenon is ascribed to the fact that the increase in horizontal effective stress is smaller than the reduction in pore water pressure. Therefore, the horizontal displacement of the enclosure structure with leakage defects caused by the pre-fall is smaller than the horizontal displacement of the enclosure structure without leakage defects.  
Figure 17: Midas finite element model of foundation pit.  
Figure 19: Horizontal displacement curve of foundation pit excavation enclosure structure with a seepage point at 0.01 m.  
Figure 18: The cloud of horizontal displacement of foundation pit excavation enclosure structure without seepage point.  
Figure 21: Horizontal displacement curve of foundation pit excavation enclosure structure with a seepage point at 0.001 m.  
Figure 22: Horizontal displacement curve of foundation pit excavation enclosure structure without seepage point.