## 3 Methodology
### Numerical Simulation  
The 3D commercial finite element software Plaxis 3D was used to establish the 3D finite element model of the foundation pit of the 'New World' project. Figure 3 illustrates the established finite element model. The size of the model was 310 m in length, 300 m in width, and 80 m in thickness. The distance of the foundation pit edge from the model boundary was more than three times the excavation depth of the foundation pit, which could effectively guarantee that the calculation of the model was not affected by the boundary effect. The model mesh was set to be ultra-fine. The tetrahedral elements were used to simulate the soil and the built-up underground structure, while plate elements were used to simulate the support piles and the diaphragm wall of the foundation pit. Point-to-point anchors were used to simulate the supports in the foundation pit, and interface elements were used to simulate the interaction between the support structure and the soil. A total of 422,376 elements were generated in the foundation pit model. The established model used the HSS small strain constitutive model to simulate the constitutive relationship of the soil and the Hoek-Brown failure criterion to the simulate the constitutive relationship of the strongly and moderately weathered rocks. According to the actual conditions of the project site and laboratory test results of on-site soil samples, the physico-mechanical parameters of typical soil profiles at the project site could be obtained, as shown in Table 2.  
The simulation of the foundation pit excavation was carried out according to the on-site construction sequence, which was divided into five batches and constructed with interval jump excavation. The specific construction steps and the simulation of the construction process are displayed in Table 3. It was worth noting that the model simulated the unloading and reloading of huge loads caused by the Yuantai Building by applying the removal and reapplication of face loads at the same time as the excavation. The model applied this face load after geo-stress equilibrium and removed the face load after the construction of condition 2. After the completion of the construction of sub-pit 3A10-2, the face load representing the Gentai Building was applied to the corresponding location on the construction site. Figure 3: Schematic diagram of the finite element model. (**a**) Model size. (**b**) Condition 1. (**c**) Condition 2. (**d**) Condition 3. (**e**) Condition 4. (**f**) Condition 5. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Layer of Soil** & **Thicknesses** & \(\gamma\) & **c** & \(\varphi\) & **E** \\ \hline  & **(m)** & **(kN/m3)** & **(kPa)** & **(\({}^{\circ}\))** & **(MPa)** \\ \hline Miscellaneous fillings & 2 & 17.5 & 8.0 & 10.0 & 4 \\ Sandy chalky soil & 3 & 18.9 & 6.3 & 32.6 & 8 \\ Silt sand & 6 & 19.5 & 3.7 & 36.6 & 14 \\ Chalky sand with sandy silt & 5 & 19.1 & 4.8 & 34.6 & 12 \\ Sandy chalky soil & 4 & 18.9 & 6.3 & 32.6 & 8 \\ Silty clay & 11 & 18.7 & 9.1 & 27.4 & 6 \\ Fine sand & 7 & 20.1 & 2.3 & 40.0 & 18 \\ Boulder & 6 & 20.0 & 3.0 & 40.0 & 30 \\ Cobble & 8 & 20.0 & 3.0 & 42.0 & 35 \\ Strongly weathered rock & 3 & 22.0 & 35.0 & 25.0 & 38 \\ Medium-weathered rock & 25 & 24.0 & 200.0 & 32.0 & 50 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Soil parameters.