## 2 Project Overview  
The project under study is for a shantytown renovation in Beijing: the surrounding environment is complex, with some existing buildings on the east side of the area and a subway station on the west side. The plots are planned to be 5 floors underground and 23 floors above ground, adopting the method of synchronous construction of the superstructure and substructure under a semi-top-down construction method. In this project, the foundation pit is 62.3 m east-west and 45.7 m north-south, and the excavation depth is set to be 25.5 m. The diaphragm walls with a depth of 36.5 m were used as the foundation pit retaining structures, and the vertical supports adopted integrated piles and columns. Figure 1 presents the relationship between the foundation pit and the existing buildings; the distance between them is 23.4 m and 32.1 m, respectively. Meanwhile, the monitoring points used to validate the numerical model in this article are also marked in Figure 1, where DB-1 and DB-2 are the two monitoring points of ground settlement, and JC-1 and JC-2 are used to monitor the building subsidence. For the convenience of analyzing the calculation results, the side walls of the pit are numbered clockwise according to I to VII. Correspondingly, the monitoring sections set perpendicular to them in the middle of each wall are numbered as I-I, II-II, III-III, IV-IV, V-V, VI-VI, and VII-VII. According to the engineering geological survey results, the site strata from top to bottom are artificial fill, sandy silt-clay silt, medium sand, silty clay, pebble layer, silty clay layer, pebble layer, and silty clay layer. Table 1 lists the property parameters of the strata. There are two major groundwaters in the site area, namely phreatic water in the middle sand layer and interstitial water in the pebble layer. The groundwaters do not corrode the concrete structures or the reinforcing steels in the reinforced concrete, and the interstitial water is located about 3 m below the bottom of the foundation pit and has little effect on the project. In the project, a method of synchronous construction of the superstructure and substructure was adopted, that is, the superstructure was constructed by the traditional bottom-up method, and the substructure was constructed simultaneously using a covered semi-top-down construction method, as shown in Figure 2. The construction processes are detailed as follows. 1. Prepare for excavation, including leveling the site, constructing the diaphragm wall, the core tubes, the pile foundations, and the steel pipe columns inside the pit;
2. To construct the water-retaining structure outside the diaphragm wall, remove the inner guide wall of the diaphragm wall, then excavate 6.7 m downwards and construct the roof of the first underground floor; \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Soil**} & \multirow{2}{*}{\begin{tabular}{c} **Thickness \(H\)** \\ **(m)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Unit Weight** \\ **\(\gamma\) (kN/m3)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Compression** \\ **Modulus** \\ **\(E_{s}\) (MPa)** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Poisson Ratio** \\ **\(\
u\)** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Cohesive** \\ **Force** \\ **\(c\) (kPa)** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Internal** \\ **Friction Angle** \\ \(\phi\) ( )** \\ \end{tabular} } \\ \hline Artificial fill & 2 & 17.9 & 3.7 & 0.30 & 5.0 & 10.0 \\ Slit & 7 & 19.1 & 8.5 & 0.30 & 31.6 & 14.3 \\ Medium sand & 13 & 20.7 & 40.0 & 0.24 & 0 & 40.0 \\ Silty clay & 2 & 19.9 & 15.7 & 0.30 & 31.2 & 14.7 \\ Pebble & 7 & 22.0 & 65.0 & 0.20 & 0 & 42.0 \\ Silty clay & 10 & 20.1 & 31.7 & 0.30 & 14.5 & 26.0 \\ Pebble & 17 & 22.0 & 75.0 & 0.20 & 0 & 42.0 \\ Silty clay & 12 & 19.8 & 35.4 & 0.30 & 15.4 & 26.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Mechanical properties of soil layers. Figure 1: Excavation site and the monitoring points.