## 3 Numerical Simulation and Analysis of Seepage Field Anomalies  
Based on the on-site detection of the foundation pit and the actual excavation condition, the influence of enclosure structure leakage on the percolation field was studied by numerical simulation. The results show that there was an anomaly in the seepage field of the foundation pit when leakage occurred. The detailed results of as follows. Considering the uncertainty in the existence of enclosure structure leakage, a two-dimensional model of the seepage field was established using Geo Studio (CnTech is the supplier) finite element software to further study the influence of the leakage of the enclosure structure on the seepage field of the foundation pit. Four calculation conditions were established, condition 1: the leakage point is 0.01 m wide; condition 2: the leakage point is 0.005 m wide; condition 3: the leakage point is 0.001 m wide; condition 4:no leakage. The geotechnical parameters are shown in Table 3, and the structural parameters are shown in Table 4. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Soil**} & \multirow{2}{*}{**Unit Type**} & \multicolumn{2}{c}{**Bulk Density**} & \multicolumn{2}{c}{**Modulus of Elasticity**} & \multirow{2}{*}{**Poisson’s Ratio**} \\  & & **(kN\(\cdot\)m\({}^{-3}\))** & & & \\ \hline steel support & truss unit & 78 & 206 & 0.26 \\ concrete bracing & truss unit & 25 & 30 & 0.20 \\ retaining piles & plate unit & 25 & 30 & 0.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Structural material parameters. Figure 6: Amount of groundwater level change at monitoring sites. The excavation method of the foundation pit is step-by-step excavation. The specific excavation steps are as follows: (1) enclosure structure establishment and perform initial ground stress balance; (2) the First precipitation to \(-6\) m, first excavation to \(-5\) m, and first concrete support; (3) the second precipitation to \(-11\) m, second excavation to \(-10\) m, and second steel support; (4) the third precipitation to \(-16\) m, the third to excavation to \(-15\) m, and the third steel support; (5) the fourth precipitation to \(-21\) m, the fourth excavation to \(-20\) m, and the fourth steel support; (6) the fifth precipitation to \(-26\) m, the fifth excavation to \(-25\) m, and the fifth steel support; (7) the sixth precipitation to \(-30\) m, the sixth excavation to \(-29\) m, and the sixth steel support. As shown in Figure 7, in the absence of leakage in the envelope structure, water level pressure difference will occur during foundation pit dewatering, and groundwater will flow around the bottom. In the case of leakage of enclosure structure, ground-water flow is disordered with the groundwater, not only flowing from the bottom of the enclosure structure around the flow, but also flowing from the leakage into the foundation pit. The drop of groundwater level increases with the increase of seepage size. As can be seen from Figures 8-11, when there is leakage in the envelope, the groundwater flow through the leakage is larger than that through the bottom of the envelope. The water flow through the leakage increases with the increase of the leakage size. The total groundwater flow into the foundation pit through the bottom of the retaining structure and the leakage is greater than the total flow into the foundation pit through the bottom of the retaining structure without leakage. In addition, the water level drop of the retaining structure with leakage is 2-3 m more than that of the retaining structure without leakage, which will promote the effective stress change of the soil around the foundation pit, and enhance the adverse impact on the surrounding environment. When the seepage is intense, a large seepage force is generated, and the water pressure at the seepage point is greater than that of the nearby part without leakage. The reason is that when there is a leakage point in the retaining structure, the difference of water head inside and outside the pit will become larger.