## 3 Establishment of Numerical Model and Selection of Calculation Parameters  
The corresponding numerical model is established in accordance with the engineering situation of the Ciqu station. The model contains both stations and foundation pits on both sides of the north and south. The diameter of the model is: 600 m in length, 200 m in width and 70 m in height. The modified M-C (Mohr-Coulomb) model in MIDAS/GTS is applied in this paper. Compared to the M-C model, the modified MC model consists of a  
Figure 3: Hydrogeological profile. Figure 2: Engineering geological profile. nonlinear elastic and elastic-plastic model with no effect between shear and compression yield, thus correcting the abnormality of pit bottom and surface uplift in the M-C model, and eliminating the problem of abnormal soil uplift in the M-C model [29]. The displacement boundary condition of the model limits the displacement of five surfaces of the model, and the ground surface is a free boundary. In the model, the rock and soil are simulated by hexahedral solid unit; the ground wall adopts dewatering plate unit in simulation, considering the relative slip between concrete and soil, interface unit between the ground wall and soil is added; the concrete support, steel support, column and waist beam are built by implanted beam unit that can automatically couple with the solid unit. The stratum in the foundation pit includes miscellaneous fill, sandy silt, fine sand, silty clay, fine sand and silty clay from top to bottom. The mechanical parameters are selected according to the practical construction, and the recommended values of relevant rock and soil mechanical parameters are shown in Table 2.  
Different from the M-C model, the main parameters of the modified M-C model involve triaxial test secant stiffness, the unloading elastic modulus, and primary consolidation loading test tangent stiffness. Thus, the soil mechanical parameters in the modified M-C model should be converted according to the Table 3.  
The obtained rock mechanical parameters and supporting structure parameters in the model according to the conversion are shown in Tables 4 and 5. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Soil Layer** & **Constitutive Model** & \(\mathbf{E_{50\text{ref}}}\)**/MPa** & \(\mathbf{E_{\text{oedref}}}\)**/MPa** & \(\mathbf{E_{\text{urref}}}\)**/MPa** \\ \hline Miscellaneous fill & Modified M-C & 3 & 3 & 9 \\ Sandy silt & Modified M-C & 11 & 11 & 33 \\ Silty fine sand & Modified M-C & 27 & 27 & 81 \\ Silty clay & Modified M-C & 13 & 13 & 39 \\ Fine sand & Modified M-C & 22 & 22 & 66 \\ Silty clay & Modified M-C & 15 & 15 & 45 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Geotechnical mechanics parameter table. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Soil Layer** & \begin{tabular}{c} **Compression** \\ **Modulus/MPa** \\ \end{tabular} & **Severe/kN/m3** & \begin{tabular}{c} **Poisson** \\ **Ratio** \\ \end{tabular} & \
\begin{tabular}{c} **Internal Friction** \\ **Angle/\({}^{\circ}\)** \\ \end{tabular} & **Cohesion/kPa** & **Thickness/m** \\ \hline Miscellaneous & 2 & 19.5 & 0.4 & 10 & 5 & 2 \\
\begin{tabular}{c} Sandy silt \\ \end{tabular} & 6 & 19.5 & 0.4 & 25 & 8 & 8.5 \\ Silty fine sand & 14 & 21 & 0.38 & 28 & 0 & 3.2 \\ Silty clay & 7 & 19.8 & 0.4 & 15 & 20 & 8.7 \\ Fine sand & 12 & 21.5 & 0.4 & 32 & 0 & 12.3 \\ Silty clay & 9 & 20 & 0.41 & 20 & 30 & 25.3 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Proposed table of geotechnical mechanical parameters.