## 3 Numerical Simulation
### Selection of Calculation Parameters  
Rock and soil layer parameters were chosen from the engineering geological survey report to guarantee the precision of the calculation outcomes. To simplify model establishment, soil layers with similar properties are consolidated into a single layer, with the thickness being the sum of the average thickness of each individual soil layer. The soil's elastic modulus E can be derived from its compression modulus Es. Using the empirical formula E = (2-5) Es, the appropriate soil elastic modulus is determined through repeated comparisons with the monitoring data, the final parameter selection is shown in Table 2.  
The elastic modulus of the tunnel lining structure material is 31,500 MPa, with a Poisson's ratio of 0.2. The foundation pit of the subway station utilizes bored piles with a diameter of 1 m and a spacing of 1.3 m. Additionally, the equivalent thickness of the diaphragm wall is adjusted to 0.8 m. The pit enclosure is supported by row piles. According to theory and engineering experience, the function of pile support is similar to that of a diaphragm wall, and the supporting piles are mainly subjected to bending moments, which means that the pile can be simplified to the corresponding thickness of diaphragm wall according to the principle of equal bending stiffness in the analysis and calculation. The specific conversion formula is as follows:  
\[\frac{1}{12}(D+t)h^{3}=\frac{1}{64}\pi D^{4} \tag{1}\]  
\[h=0.838D\sqrt[3]{\frac{1}{1+\frac{t}{D}}} \tag{2}\]  
In this formula, \(D\) is the diameter of the support pile (m); \(t\) is the clear distance between piles (m); and \(h\) is the equivalent thickness of the ground wall (m). The calculation schematic is shown in Figure 8. \begin{table}
\begin{tabular}{c c c c c c c} \hline \multirow{2}{*}{**Name**} & \multirow{2}{*}{**Gravity**} & **Poisson’s** & **Compressive** & **Elastic** & **Cohesion** & **Internal** \\  & & **Ratio** & **Modulus** & **Modulus** & **Friction Angle** \\ \cline{2-7}  & \(\gamma\)**/(KN/m3)** & \(\mu\) & \(E_{\text{S0.1-0.2}}\)/(MPa)** & \(E\)**/MPa** & \(C\)**/kPa** & \(\varphi\)\(t\)\({}^{\circ}\) \\ \hline Miscellaneous fill & 18.5 & 0.2 & 4.8 & 10 & 7.8 & 15 \\ Silty clay & 19.4 & 0.28 & 7.8 & 19.5 & 26 & 19.1 \\ Strong weathered & 21 & 0.26 & - & 70 & 40 & 28 \\ mudstone & 25.2 & 0.12 & - & 6400 & 170 & 36 \\ mudstone & 24.5 & 0.15 & - & 3500 & 90 & 35 \\ \hline \end{tabular}
\end{table} 
Table 2: Geotechnical material parameters. Figure 8: Schematic diagram of converted thickness of row piles and equal flexural rigidity of ground-connected wall. The foundation pit of this subway station employs bored piles with a diameter of 1 m and a spacing of 1.3 m, and the equivalent thickness of the ground-connected wall is converted to 0.8 m according to the above Formula (2). Details of the parameters of the foundation pit retaining structure are provided in Table 3.  
In the actual project, the steel support will be designed according to the specification of the corresponding preloaded axial force, which has a certain impact on the deformation of the pit enclosure structure, and cannot be ignored in the simulation. Methods for simulating the preloaded axial force of the steel support in ABAQUS mainly include the heating method, the Rebar method, and the initial stress method, among which the heating method is relatively simple to operate and the most common application. Therefore, this paper adopts the heating method to simulate the application of preloaded axial force on the steel support. The basic principle is to define the coefficient of linear expansion of the steel support material, change its temperature field, and apply the temperature load to the steel support, so as to achieve the effect of preloaded axial force.