## 4 SoilWorks Numerical Simulation
### Sensitivity Analysis
#### 4.3.1 Description and Input Parameter Selection for Case 3  
* Site Description The site is located at the intersection of Beixin Road Section 3 and Fuixing Road in Xindian District, New Taipei City. It has an irregular shape with an area of approximately 9533 m\({}^{2}\) and a height difference of less than 1 m (Chung-Lien Engineering Consultant Corporation, New Taipei City, Taiwan. [50]). * Subsurface Strata The subsurface conditions at the site can be divided into four layers from top to bottom (Chung-Lien Engineering Consultant Corporation [50]). A brief description of the general characteristics of each layer is provided, and the simplified engineering parameters for the subsurface layers are shown in Table 13. The groundwater investigation data for the site indicate that the groundwater level is generally around GL.\(-\)11 m. For the analysis, the initial groundwater level is set at 11 m below the ground surface. (1) Fill layer: Consists of yellow-brown sandy clay, silty clay, and silty clay with mud. The thickness is approximately 4.3 m, and the \(N\)-values range from 1 to 19. (2) Gravel layer: Contains egg-sized gravel interbedded with yellow-brown silty clay. The thickness is approximately 11 m, and the \(N\)-values range from 15 to above 50. (3) Gray sandy clay layer: Consists of gray sandy clay, silty clay, and sandy clay. The thickness is 9.6 m, and the \(N\)-values range from 7 to 50 (increasing to 50 when encountering gravel). Gravel layer: Contains egg-sized gravel interbedded with yellow-brown silty sand. The thickness is greater than 8.8 m, and the \(N\)-values are all above 50. * Foundation Excavation Plan (1) Geotechnical facilities: The excavation depth is 14.6 m, and the foundation type is a raft foundation. The retaining structure consists of 80 cm thick continuous walls, with a depth of 23.5 m. (2) Support system: The inverted construction method is adopted for the site, which involves staged excavation and construction of underground floor slabs. The support structures used during the excavation process are 1F, B2 FL, and B3 FL. (3) Excavation steps: The excavation is carried out in four stages. In the first stage, the excavation is lowered to GL.\(-\)2.5 m to construct the 1F floor slab. In the second stage, the excavation is lowered to GL.\(-\)8.0 m to construct the B2F floor slab (GL.\(-\)7.025 m). In the third stage, the excavation is lowered to GL.\(-\)11.2 m to construct the B3F floor slab (GL.\(-\)10.225 m). Finally, in the fourth stage, the excavation is lowered to the final excavation bottom at GL.\(-\)14.6 m.
* Determination of Soil and Structural Parameters Based on the recommended engineering parameters listed in Table 13, the soil input parameters used in the program are shown in Table 12. The retaining walls and floor slabs are simulated using beam elements. The main input data include a cross-sectional area (\(A\)), Young's modulus (\(E\)), and the moment of inertia (\(I\)). The stiffness of the retaining wall is generally reduced by 70% based on empirical experience, while the stiffness of the floor slab is reduced by 25%. The input parameters for the structural elements are shown in Tables 13 and 14. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Depth (m)**} & **Soil Classi-** & **Use \(N\)** & \(\epsilon^{\prime}\) & \(\Phi^{\prime}\) & \(\gamma_{\text{\emph{unstat}}}\) & \(\gamma_{\text{\emph{sat}}}\) & \(E_{\mathcal{S}}\) & \(\
u\) \\  & **fication** & **Value** & **(kN/m\({}^{2}\))** & **(\({}^{\circ}\))** & **(kN/m\({}^{3}\))** & **(kN/m\({}^{3}\))** & **(kN/m\({}^{2}\))** & \\ \hline
0.0–4.0 & SF, ML, CL & 18 & 0 & 28 & 20.1 & 20.0 & 44,100 N & 0.347 \\
4.0–15.7 & GW & 44 & 4.9 & 38 & 22.1 & 22.3 & 2450 N–3430 N & 0.263 \\
15.7–20.3 & ML, SM & 18 & 0 & 31 & 20.0 & 19.3 & 44,100 N & 0.327 \\
24.4–33.0 & GW & 100 & 9.8 & 40 & 22.1 & 22.3 & 2450 N–3430 N & 0.263 \\ \hline \hline \end{tabular}
\end{table} 
Table 12: Soil strength parameter input table for Case Study 3 in SoilWorks.