## 4 Results and Discussion  
### Selection of Key Constitutive Parameters  
Figure 5 is the result of the horizontal displacement of the retaining wall calculated by the empirical parameters of the constitutive model (Table 1). In the level 4, 3, and 2 excavation stages, the horizontal displacements of the retaining wall calculated by the empirical values of the constitutive model are roughly consistent with the measured value with respect to the curve shape. This indicates that the selected constitutive models for the soil layers can effectively characterize the deformation of the retaining wall caused by the braced excavation. The HS model is suitable for silt, and the HSS model is suitable for clay in this case. However, the calculated values in each excavation stage are quite different from the measured values, and these differences are the largest at the excavation face. The calculated value overestimates the lateral displacement of the retaining wall, indicating that the value of the initial soil parameters is seriously underestimated. Specifically, in the level 4, 3, and 2 excavation stages, the relative error between the calculated value and the measured value of the maximum horizontal displacement is 52%, 65%, and 71%, respectively. According to the inherent soil variability, the predicting accuracy of the maximum horizontal displacement of the retaining wall should be within \(\pm\)15% [31]. Therefore, the simulated result using the constitutive parameters determined by the soil survey report and the engineer's design experience overestimates the horizontal displacement of the retaining wall, which cannot meet the requirements of prediction accuracy. Figure 5: Horizontal displacement of the retaining wall and the measured values. \begin{table}
\begin{tabular}{c c} \hline \hline
**Calculation Phase** & **Construction Activity** \\ \hline
1 & Self-weight stress generation \\ \hline
2 & Tunnel construction (displacement reset) \\ \hline
3 & Construction of the diaphragm wall \\ \hline
4 & Excavation level 1 (\(-\)1.9 m) \\ \hline
5 & Installation of the first brace \\ \hline
6 & Excavation level 2 (\(-\)5.9 m) \\ \hline
7 & Installation of the second brace \\ \hline
8 & Excavation level 3 (\(-\)9.9 m) \\ \hline
9 & Installation of the third brace \\ \hline
10 & Excavation of foundation pit 4 (\(-\)13.9 m) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Construction stages. In order to improve the accuracy of numerical simulation, the large strain parameters \(E_{50}^{ref}\), \(E_{oed}^{ref}\) and \(E_{uu}^{ref}\) shown in Table 1, which mainly control the deformation of soil, were selected as candidate important parameters to optimize the large strain response of the simulation. Meanwhile, the small strain parameters \(G_{0}^{ref}\) and \(\gamma_{0.7}\), which control the shape of the shear stiffness degradation curve, were also selected as candidate important parameters. By the sensitivity and correlation analysis of these five important parameters, the key constitutive parameters controlling the deformation of the braced excavation can be determined. Figure 6 shows the sensitivity analysis of five important parameters for the sandy silt layer, muddy clay layer, and silty clay layer. The y axis of Figure 6 represents the relative change rate, which is defined as \(100\%\times 1\) the changed value--the original value / the original value. The relative change rate reflects the impact of changing the constitutive parameters on the maximum horizontal displacement of the retaining wall during the fourth stage of braced excavation. The higher the relative change rate is, the more sensitive the parameter is. It can be seen that \(G_{0}^{ref}\) and \(\gamma_{0.7}\) are the most sensitive parameters among all parameters. Among the three soil layers, \(E_{50}^{ref}\) is the most sensitive large strain parameter, which is consistent with the existing work [28]; _re fur_ is the second-most sensitive large strain parameter, which is slightly more sensitive than \(E_{oed}^{ref}\).