## 3 Numerical Model  
### Finite Element Model  
ABAQUS finite element software is used to simulate the whole construction process of the foundation pit group, and the corresponding numerical model is established considering the requirements of design and construction. Due to the complexity of construction and geological conditions, in order to balance the modeling and calculation efficiency, the following approaches are adopted: (a) simplify the characteristics of stratum distribution, keep each stratum horizontal, and adopt average thickness; (b) ignore the influence of interlayer soil and assume that all the stratum are homogeneous; (c) consider all soil layers as normally consolidated soil; (d) assume that the diaphragm wall, the support pile, the concrete cushion, and internal support are elastic.  
According to existing research results, the horizontal influence range of the foundation pit is 3-4 times the excavation length and width, and the influence range in the depth direction is 2-4 times the excavation depth. In order to minimize the boundary effect, the size of the 3D finite element model is determined to be 700 m \(\times\) 520 m \(\times\) 90 m. To balance the calculation accuracy and efficiency, the grid size is set to gradually increase from the foundation pit to the boundary of the calculation domain [22]. The side boundary of the calculation domain is set as a vertical displacement constraint, the bottom boundary is set as a fixed displacement constraint, and the top boundary remains free. In order to obtain more realistic simulation results, it is considered that the influence of dewatering  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Soil/Rock** & **Thickness (m)** & \begin{tabular}{c} **Unit Weight** \\ **(d-N/m)** \\ \end{tabular} & \begin{tabular}{c} **Compressive** \\ **Modulus (MPa)** \\ \end{tabular} & **Poisson’s Ratio** & **Cohesion (kPa)** & \
\begin{tabular}{c} **Friction** \\ **Angle (°)** \\ \end{tabular} &
\begin{tabular}{c} **Permeability** \\ **Coefficient (cm/s)** \\ \end{tabular} \\ \hline Miscellaneous fill & 3 & 1990 & 4.1 & 0.30 & 15 & 12 & \(2\times 10^{-3}\) \\ Pain fill & 3 & 1790 & 3.77 & 0.35 & 19 & 16 & \(2.5\times 10^{-5}\) \\ Mucky silty clay & 25 & 1760 & 3.57 & 0.30 & 10.6 & 18.2 & \(5\times 10^{-6}\) \\ Clayey silt & 13 & 1770 & 4.2 & 0.35 & 10.8 & 19.8 & \(4\times 10^{-6}\) \\ Fine silt sand & 11 & 1840 & 11.2 & 0.28 & 2.3 & 33.9 & \(1.63\times 10^{-3}\) \\ Limestone & 25 & 2750 & - & 0.36 & 800 & 40 & - \\ \hline \hline \end{tabular}
\end{table}
Table 1: Main physical and mechanical parameters of the soil/rock layer.  
on deformation development cannot be ignored. Therefore, the dewatering calculation is considered in the model, and eight nodes hexahedral element coupled pore water pressure (C3D8P) is adopted for the soil. Eight nodes hexahedral incompatible element (C3D8I) is adopted for the diaphragm wall to improve calculation accuracy. Beam unit (B31) is adopted for internal support [22]. The initial groundwater burial depth of the model is set as 1 m, the top boundary allows free drainage, and the sides are set as constant heads to simulate groundwater recharge. The 3D finite element model is shown in Figure 2.