## 3 Numerical Simulation of Deep Foundation Pit
### Analysis of Numerical Results  
Figure 6 presents the horizontal displacement nephogram of the diaphragm wall in the y-direction and the ground surface settlement nephogram following the excavation of the foundation pit. During the final excavation stage, the horizontal displacement of the diaphragm wall presented a \"bow-shaped\" pattern, characterized by a significant displacement in the middle and lesser displacements at both sides. This behavior aligns with the deformation characteristics of the diaphragm wall in open-cut foundation pits. Further analysis revealed that the ground surface settlement shows a typical \"concave groove\" shape. Moreover, the use of the top-down construction method, where the roof of the main structure was poured before backfilling, prevented post-construction settlement of the backfilled soil. Instead, it exhibited a heaving phenomenon. This upward heaving \begin{table}
\begin{tabular}{c c} \hline
**Analysis** & **Description of Working Condition** \\
**Conditions** & **Description of Working Condition** \\ \hline Stage 1 & Geostatic equilibrium \\ Stage 2 & Construction of upper enclosure structure \\ Stage 3 & Ground wall and lattice column construction (displacement reset) \\ Stage 4 & Excavation 1 (\(-\)3.0 m) \\ Stage 5 & The first-floor main structure construction \\ Stage 6 & Backfill traffic \\ Stage 7 & Excavation 2 (\(-\)11.7 m) \\ Stage 8 & The second-floor main structure construction \\ Stage 9 & Excavation 3 (\(-\)19.5 m) \\ Stage 10 & The third-floor main structure construction \\ Stage 11 & Excavation 4 (\(-\)28.2 m) \\ Stage 12 & The fourth floor main structure construction \\ \hline \end{tabular}
\end{table} 
Table 4: Finite element analysis conditions. Figure 5: Measured and simulated horizontal displacement at ZQT82 monitoring points. was attributed to the fact that as the excavation progressed and unloading took place at the foundation pit's bottom, the soil heaved upward in response to the excavation. Consequently, the lattice columns also experienced upward heaving, which was greater than the settlement transmitted downward due to the construction of the upper structure. This disparity primarily accounted for the differential settlement between the diaphragm wall and the lattice columns. Future research should focus on strategies to control such differential settlement during the design and construction stages. To investigate the stress and deformation characteristics of the foundation pit under different top-down construction conditions, deformation data were extracted at different construction stages, as shown in Figure 7. It was observed that with the excavation of the foundation pit, the horizontal displacement of the diaphragm wall gradually increased, and the depth at which the maximum value occurred gradually moved downward. Further analysis revealed that the majority of the diaphragm wall's deformation increment, resulting from excavation, primarily occurred below the cast-in-place floor slab, while no significant displacement was observed above this slab. This phenomenon arose because, in the top-down construction method, the floor slab was poured first, and subsequent excavation was conducted only after the slab reached its designed strength. The reinforced concrete utilized for the floor slab possessed high strength and good integrity, which effectively restricted the deformation of the diaphragm wall situated above the floor slab. The maximum horizontal displacements of the diaphragm wall at different excavation stages were 2.01 mm, 11.81 mm, 26.48 mm, and 46.89 mm, respectively. Figure 6: Deformation nephogram of foundation pit at final excavation stage. Figure 7b revealed that the ground surface settlement gradually increased as the foundation pit was excavated, which was consistent with the change trend of the diaphragm wall displacements. The main influence range of the ground surface settlement caused by excavation extended approximately 0 to 56 m away from the foundation pit boundary, corresponding to about twice the excavation depth.