## 3 Methodology  
The ABAQUS software was used to simulate the whole construction process. The shape of the foundation pit in this project is complex and irregular, so the size of numerical model was determined based on the maximum size of the foundation pit in each direction, which was 62.3 m in the east-west direction, 45.7 m in the north-south direction, and 25.5 m in the excavation depth. For eliminating the effects of the model boundaries on the calculation results, the model calculative height (in the z-direction), length (in the x-direction), and width (in the y-direction) were set to be 70.0 m, 170.0 m, and 110.0 m, respectively, and the boundary conditions of the model were set as follows: the top surface was free, while the bottom surface was fixed by constraining all the degrees of freedom of the nodes on it. The nodes on the side surface were allowed to have vertical displacement, but their normal displacements were frozen.  
The finite-element model for the excavation area and surrounding site is shown in Figure 3a,b which present the structure of the excavation area.  
In the finite-element model, the soil, the diaphragm wall, and the core tubes were modeled using the solid elements. The 2D plate elements were used to simulate the behavior of the slabs and the side walls. The piles and columns were simulated with the 1D beam elements. In this study, the Mohr-Coulomb model was chosen to describe the stress-strain relationship of the soils. The modulus of deformation used was calculated from Equation (1) using the parameters in Table 1 according to the literature [25].  
\[E_{0}=\beta\quad E_{s} \tag{1}\]  
where \(\beta=1\quad 2 vK_{0}=(1+v)(1\quad 2v)(1\quad v)\), \(E_{0}\) is the modulus of deformation, \(E_{s}\) is the compression modulus, and \(v\) is the Poisson ratio.  
In the practical engineering, the materials for the diaphragm wall, core tubes, slabs, side walls, piles are all reinforced concrete, and the columns are made of steel tube concrete. Considering that the possibility of plastic deformation of structural components under normal excavation construction is very small, and for the convenience of calculation, material equivalence was performed on the diaphragm wall, core tubes, slabs, side walls, piles, and columns in this study, all of which were assumed to be elastic components. According to the engineering design scheme, the material parameters of the structure components during the excavation process are shown in Table 2.  
Due to the lack of relevant information on the surrounding buildings, this study only analyzes the influence of loads of the adjacent existing buildings, by applying the weight of existing buildings to the corresponding ground surface in the form of loads. The loads of the existing buildings and that of the new superstructure constructed were all taken as  
Figure 3: The FEM model. (**a**) Excavation and surrounding site; (**b**) structure in the excavation area.  
20 kPa per story. Since the project construction area was far from the subway tunnel, the effect of the subway tunnel was ignored in this study, while the effect of groundwater was also not considered.  
Given that it is difficult to achieve ground stress equilibrium when existing buildings are simulated in the form of loads. In this study, ground stress equilibrium was performed only for the initial geological condition, and then the influence of existing buildings was eliminated by phase subtraction to achieve the zeroing of the initial displacement field of the model before the construction of the foundation pit. According to the actual construction situation, the numerical simulation process is listed in Table 3. The construction process was realized by deactivating and reactivating elements in ABAOUS software.