## 5 Conclusions  
This paper describes a foundation pit project adjacent to a subway tunnel. The foundation pit has a complex geometry, deep excavation depth and large excavation area, and has very high requirements for support systems to resist deformation. Due to the development cycle, demolition and other reasons, the entire foundation pit is excavated in two sections, A and B, and the time and space effect of the excavation is significant. There are subway lines in operation within 12 m west of the basement exterior wall on the west side of the foundation pit, and the tunnel burial depth is less than the excavation depth of the foundation pit. In order to explore the influence of foundation pit excavation on the adjacent subway, MIDAS/GTS software is used to establish a finite element model for the excavation of section A and section B, and the rationality of the finite element results is  
Figure 13: Maximum horizontal deformation of subway tunnel caused by foundation pit construction. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Simulation Conditions** & \begin{tabular}{c} **Simulation Value** \\ **Caused by Section A** \\ **(mm)** \\ \end{tabular} & \begin{tabular}{c} **Monitoring Value** \\ **Caused by Section A** \\ **(mm)** \\ \end{tabular} & \begin{tabular}{c} **Simulation Value** \\ **Caused by Section B** \\ **(mm)** \\ \end{tabular} & \begin{tabular}{c} **Monitoring Value** \\ **Caused by Section B** \\ **(mm)** \\ \end{tabular} \\ \hline Excavation to elevation \(-2.20\) & \(0.02\) & \(0.03\) & \(0.05\) & \(0.08\) \\ \hline Excavation to elevation \(-8.15\) & \(0.085\) & \(0.1\) & \(0.15\) & \(0.22\) \\ \hline Excavation to elevation \(-12.95\) & \(0.15\) & \(0.25\) & \(0.28\) & \(0.39\) \\ \hline Excavation to elevation \(-17.75\) & \(0.27\) & \(0.37\) & \(0.37\) & \(0.5\) \\ \hline Excavation to the design & & & & \\ elevation of the bottom of the & \(0.30\) & \(0.42\) & \(0.42\) & \(0.54\) \\ \hline \begin{tabular}{c} Remove the fourth layer of \\ support \\ \end{tabular} & \(0.36\) & \(0.45\) & \(0.48\) & \(0.61\) \\ \hline \begin{tabular}{c} Remove the third layer of \\ support \\ \end{tabular} & \(0.39\) & \(0.5\) & \(0.50\) & \(0.65\) \\ \hline \
\begin{tabular}{c} Remove the second layer of \\ support \\ \end{tabular} & \(0.45\) & \(0.58\) & \(0.56\) & \(0.71\) \\ \hline
\begin{tabular}{c} Remove the first layer of \\ support \\ \end{tabular} & \(0.49\) & \(0.63\) & \(0.62\) & \(0.75\) \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Maximum horizontal deformation of subway tunnel caused by pit construction. verified by monitoring the tunnel. Based on the above discussion, the following conclusions are finally drawn:  
The enclosure structure of the foundation pit adopts rotary cast-in-place piles, and the support system adopts four-layer (local three-layer) reinforced concrete rectangular inner support. According to the monitoring results, this foundation pit support system can well limit the settlement around the road, the horizontal displacement of the ring beam, and the deep soil displacement of the foundation pit. At the same time, the axial force of the inner support is always maintained at a relatively safe level. Compared with the underground diaphragm wall, the support system saves 20 million yuan in project cost and about 3 months in the construction period while meeting the deformation requirements;  
According to the finite element calculation results, the horizontal displacement of the subway tunnel is generally smaller than the vertical displacement. Therefore, vertical deformation should be the focus of tunnel deformation monitoring. The maximum vertical displacement of the subway tunnel caused by the excavation of the foundation pit in section A and section B is 2.45 and 2.61 mm, and the maximum horizontal displacement of the subway tunnel caused by the excavation of the foundation pit in section A and section B is 0.49 and 0.62 mm. The maximum vertical displacement and horizontal displacement are both less than the specification limit value of 10 mm.