## 3 Numerical Simulation of Deep Foundation Pit
### Analysis of Numerical Results
The secondary influence area spans approximately 56 to 75 m away from the boundary, which is about 2.7 times the excavation depth. The maximum ground surface settlements at different excavation stages were \(-18.11\) mm, \(-26.29\) mm, \(-37.14\) mm, and \(-51.30\) mm, respectively. To investigate the differential settlement between the diaphragm wall and the lattice columns during the top-down construction process, the vertical displacements of both the diaphragm wall and the lattice columns at various excavation stages were extracted to calculate their differential settlement, as presented in Table 5.  
As previously noted, the primary challenges during the top-down construction process include the differential settlement and the resulting stress redistribution within the main structure. During the construction process, the pouring and solidification of concrete generally require significant time. Therefore, when the first layer of the main structure  
Figure 7: Deformation nephogram of foundation pit under different excavation scenarios. was poured, the diaphragm wall and the lattice column can be viewed as independent components. The vertical displacements of the diaphragm wall and the lattice column were designated as the baseline for subsequent analysis. This assumption implies that any displacement at this point is considered negligible. Table 5 depicts that during the initial excavation stage, the vertical displacements of the lattice column and the diaphragm wall were \(-1.23\) mm and \(-0.98\) mm, respectively, resulting in a differential settlement of only \(0.25\) mm. This finding indicated that during the initial excavation stage, the soil unloading rebound induced by the foundation pit excavation was relatively small. This allowed for effective integration between the diaphragm wall and the lattice column, which contributed to the control of differential settlement. As excavation progressed, both the vertical displacements of the diaphragm wall and the lattice column showed a gradual increase, while the differential settlement initially decreased and then increased. This behavior was primarily attributed to the excavation of the foundation pit, which reduced the friction between the diaphragm wall and the surrounding soil. Concurrently, the excavation unloading effects at the pit bottom resulted in an increase in heaving, which is illustrated in Figure 6b. However, the pouring of the main structure led to further compression of the lattice columns, thereby restricting their heaving. This results in a deformation pattern for the lattice column characterized by compression in the upper section and heaving in the lower section, as depicted in Figure 8. Analysis of Figure 8 confirmed that the maximum settlement of the lattice column occurred at its top, resulting in the largest differential settlement between the upper main structure and the diaphragm wall. The differential settlement initially decreased and then increased during the excavation process. This behavior showed that during the initial excavation stage, the diaphragm wall and the lattice column remained relatively independent. Subsequently, both the diaphragm wall and the lattice column reached a phase of relative stability in terms of their settlements. However, as excavation continued, they exhibited signs of separation once again. Figure 8: Vertical deformation nephogram of lattice column at final excavation stage. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Working Condition**} & **Maximum Vertical** & **Maximum Vertical** & \\  & **Displacement of Ground** & **Displacement of Lattice** & **Difference Value** \\  & **Wall** & **Column** & \\ \hline The first-floor main structure construction & — & — & — \\ The second-floor main structure construction & \(-1.23\) & \(-0.98\) & \(0.25\) \\ The third-floor main structure construction & \(-1.51\) & \(-1.64\) & \(0.13\) \\ The fourth-floor main structure construction & \(-3.76\) & \(-3.02\) & \(0.74\) \\ \hline \hline \end{tabular}
\end{table}