## 2 Project Background
### Geological and Hydrogeological Data  
The proposed regional site is located in the coastal area of southeastern Zhejiang Province, which is characterized by a mid-subtropical maritime monsoon climate. The climate is mild, with four distinct seasons, abundant rainfall, ample sunshine, and a lack of severe cold in winter or extreme heat in summer. According to meteorological records, the average annual temperature in the region is 17 \({}^{\circ}\)C, with an extreme maximum temperature of 38.1 \({}^{\circ}\)C and an extreme minimum temperature of \(-6.8\)\({}^{\circ}\)C. Precipitation is irregularly distributed both between and within years, with a concentration of rainfall during the plum rain season from April to June and the typhoon season from July to September. The multi-year average precipitation is 1558.47 mm, with a maximum annual precipitation of 2375.1 mm and a minimum annual precipitation of 912.8 mm. The area belongs to the Huangyan-Xiangshan Fault Zone of the Southeastern Zhejiang Uplift of the South China Fold System, which is dominated by fracture structures which spread mostly in the north-northeast and north-east direction. The base comprises Late Paleozoic strata of light metamorphic rocks, and the upper part consists of Mesozoic volcanic rocks with significant thickness. There is no regional large fracture passing through, the fold structure is not developed, and the north-east-oriented Taishun-Huangyan Large Fracture and Wenzhou-Zhenhai Large Fracture pass through from the west side of the site. The thickness of the Quaternary strata at the project site is large, and the regional fractures are far away. There is no active fault passing through the site and its vicinity, and the regional geological structure has no influence on the project. The site's geomorphological type is a Quaternary Marine Plain landform with river ponds located in the northeast corner and an original ditch connected to an external river. Most of the ground sections are composed of construction waste from demolition and recent artificial landfill residue, and the topography is slightly undulating. The soil layer in the depth range of 94 m below the ground level of the site can be divided into eight engineering geological layers. Table 2 presents the physical and mechanical parameters of each soil layer. By conducting triaxial tests on soil, the cohesion and internal friction angle can be obtained. Through compression tests, the compressive modulus can be obtained. The parameters in this paper come from a water content test, density test, specific gravity test, consolidation test, and triaxial compression test, in the \"Standard for geotechnical testing method\". The groundwater at the site occurs mainly as pore phreatic water and confined water. The pore phreatic water is mainly stored in the upper clay layer, and the groundwater \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Geological** & **Layer** & \begin{tabular}{c} **Unit** \\ **Thickness (m)** \\ \end{tabular} & \begin{tabular}{c} **Cohesion \(c\)** \\ **Weight** \\ \end{tabular} & \
\begin{tabular}{c} **Internal Friction** \\ **Angle \(\varphi\)** \\ \end{tabular} &
\begin{tabular}{c} **Compressive** \\ **Modulus \(E_{\text{s}}\)** \\ **(MPa)** \\ \end{tabular} \\ \hline Clay & 0.6–5.8 & 18.3 & 27.5 & 13.6 & 3.3 \\ Muddy & 14.5–30.4 & 16.5 & 10.0 & 8.0 & 2.1 \\ Clay & 0.0–7.9 & 16.8 & 20.2 & 11.6 & 2.5 \\ Clay & 3.0–17.2 & 18.2 & 27.5 & 15.9 & 4.0 \\ Slit & 1.7–20.0 & 18.0 & 27.6 & 14.0 & 3.6 \\ Silty clay & 0.0–20.4 & 18.5 & 31.9 & 15.8 & 5.5 \\ Silty clay & 0.0–4.1 & 19.5 & 37.0 & 18.5 & 7.25 \\ Fine sand & Unpenetrated & 19.5 & - & - & 10.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Physical and mechanical parameters of soil layers. recharge is primarily from atmospheric precipitation and surface water runoff.