# Research on Construction Sequencing and Deformation Control for Foundation Pit Groups
## 3 Results
### Pit Spacing Parametric Analysis  
The following analysis supplements the previous study on the influence of foundation pit spacing during synchronous excavation of adjacent foundation pits. A parametric analysis is conducted to investigate the effect of different pit spacings on the deformation of diaphragm walls. The analysis is performed using PLAXIS 3D software, where a three-dimensional finite element model is established at the same scale as the model tests. The ratios of B/He (spacing between adjacent pits/excavation depth) are set to 0.2, 0.6, 1, and 1.4. Given the excavation depth of 0.6 m in this test, the corresponding separation zone widths are 120 mm, 360 mm, 600 mm, and 840 mm, which serve as reference values, as shown in Figure 16.  
Table 3 lists the parameter values for sandy soil. To validate the feasibility of the soil parameter selection method, the measured data for diaphragm walls 2# and 3# during synchronous excavation of adjacent foundation pits were analyzed. Simulation results using two parameter sets were compared with measured values, as shown in Figure 17, which presents the horizontal displacements of the retaining structure. The curves demonstrate that the modified HSS constitutive model, incorporating small-strain stiffness characteristics, aligns better with the measured data. Thus, it more accurately simulates the deforma  
Figure 15: Horizontal displacement diagrams under synchronous excavation conditions. tion behavior of the retaining structure during excavation. The numerical results also match the experimental deformation trends, confirming the feasibility of the constitutive model. As shown in Figure 18, the earth pressure distribution behind the diaphragm wall under four separation zone widths is presented. The figures indicate that the earth pressure generally decreases as excavation progresses. For larger finite soil widths, the retaining structure experiences greater deformation per soil layer unloading, but the reduction in earth pressure is smaller. For example, at a width-to-depth ratio of 1.4, the earth pressure at the wall toe decreases only from 7.95 kN/m2 to 6.69 kN/m2 by the end of excavation. In contrast, for smaller finite soil widths, the incremental deformation of the diaphragm wall decreases, but the reduction in earth pressure becomes more significant. For instance, at a width-to-depth ratio of 0.2, the earth pressure at the wall toe decreases from 7.05 kN/m2 to 5.5 kN/m2 by the end of excavation. Figure 16: Model construction. Figure 17: Comparison of simulated and measured horizontal displacements. \begin{table}
\begin{tabular}{l l} \hline \hline
**Parameter Group** & **Parameters and Values** \\ \hline Stiffness Parameters & \(E_{50}^{\text{ref}}=30\) MPa, \(E_{\text{oed}}^{\text{ref}}=30\) MPa, \(E_{\text{ur}}^{\text{ref}}=90\) MPa \\ \hline Material Parameters & \(m=0.5\), \(\
u=0.2\), \(K_{0}=0.33\) \\ \hline Strength Parameters & \(c^{\text{ref}}=0\) kPa, \(\varphi=42^{\circ}\), \(\psi=16^{\circ}\) \\ \hline Shear Moduli & \(G_{0}^{\text{ref}}=104.6\), \(G_{0}^{\text{ref}}\) (correct) = 133.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Values of physical and mechanical parameters for sandy soils. From the figures, it can be observed that the distribution of earth pressure after excavation exhibits similar trends under different separation zone widths. The distribution curve shows an inflection point near the excavation face. Above the inflection point, the earth pressure distribution is nonlinear and gradually decreases as excavation progresses. Below the inflection point, the earth pressure on the diaphragm wall follows a linear distribution, with a slope consistent with that of the at-rest earth pressure line. As the foundation pit spacing decreases, the earth pressure curve deviates further from the at-rest earth pressure value. Conversely, as the foundation pit spacing increases, the earth pressure curve approaches the at-rest earth pressure. When the foundation pit spacing exceeds 0.6 times the excavation depth (i.e., B/He?