## 4 Numerical Simulation  
### D Numerical Model  
The finite element software is used to simulate the excavation of the foundation pit. To simplify the calculation and eliminate the influence of the model size effect, 1/4 of the foundation pit is chosen for modeling. The model size is 216 m \(\times\) 105 m \(\times\) 55 m. Figure 10 shows the 3D finite element model. All soil layers are modeled using the hardening soil (HS) model. The HS model considers not just the non-linear features of soil, but also the complex stress patterns associated with deep foundation construction. Compared with other soil principal structure models, the hardened soil principal structure model is more suitable for the calculation and analysis of deep foundation works [26; 27]. At the same time, the model was considered to have the following assumptions: (1) the relative slip generated on the contact surface between the support structure and the surrounding soil is not considered, and they are considered to be in a state of coordinated deformation at all times; (2) only the initial stresses in the self-weight stress field are considered and the tectonic stress field is not considered, so that the soil layer reaches equilibrium under self-weight and then the excavation of the pit is simulated; (3) the sequence of construction steps is used to simulate the whole construction process.  
The embedded beam unit is used to simulate soil nail support. The top of soil nailing is set as a rigid connection model with the concrete wall so that its displacement and rotation are consistent. The main parameters of soil nailing are shown in Table 3. The slope hanging shotcrete and the same row of bored piles are simulated by the plate element, and the relevant parameters are shown in Table 4. The equal stiffness substitution between the same row of bored piles and the plate is calculated by the following formula [28]:  
\[\frac{1}{12}(D+t)h^{3}=\frac{1}{64}\pi D^{4}, \tag{1}\]  
where \(D\) is the diameter of the bored cast-in-place pile; \(t\) is the net distance between the two piles; \(h\) is the thickness of the equivalent plate.  
Figure 10: 3D finite element model.  
The bolt element simulates the prestressed anchor cable's free part, whereas the embedded beam element simulates the anchoring section. Table 5 shows the main parameters. The interface element simulates the interaction between soil and structure. The discounting factor for interface strength \(\mathrm{R_{inter}}\) takes into account the soil's cohesion and internal friction angle, and the interface represents the strength relationship between soil and structure through the discounted internal friction angle and cohesion [12], with \(\mathrm{R_{inter}}\) set at 0.65.  
Due to the precipitation measures taken before construction, the influence of groundwater is not under consideration during the simulation process. The mesh is divided using a finite element mesh cell with 10-node tetrahedral cells. Boundary conditions of the model are established in accordance with actual circumstances. The four sides of the model have fixed constraints, the bottom of the model has fixed restrictions and the top surface of the model is free. Figure 11 represents the model's three-dimensional mesh. The specific processes of slope excavation, soil nail wall construction, and shotcrete surfacing are not discussed in this paper.