## 3 Field Experiments  
To investigate the 3D flow and nonlinear flow phenomenon near the diaphragm wall and the pumping well, field multi-depth pumping tests were executed. The pumping tests took place in the foundation pit of Qianjiang Century City Station. A total of 34 pumping wells were installed within the pit, with 19 of them located in Pit A (labeled YA1-19) and the remaining 15 in Pit B (labeled YB1-15). During the tests, one well was subjected to pumping, while the others, which had not been tested, served as observation wells. Additionally, observation wells (i.e., H2 and YW1) were established outside the foundation pit to monitor the impact of the pumping test on the nearby groundwater. Pore pressure gauges were also installed along the exterior of the observation well to track the changes in groundwater pore pressure at varying depths. The KXR-3031 vibrating string pore pressure gauge was used in pore pressure monitoring. The measurement threshold was 0.4 MPa, and the precision was 0.05%F.S. Before installation, the pore pressure gauges were fully saturated with water. A borehole was drilled at the predetermined position, and the filter tube of the pumping well was inserted. Filter material was filled between the filter tube and the borehole wall and measured continuously up to the designated depth of a pore pressure gauge. The pore pressure gauge, covered in cotton cloth, was then installed down to its position. More filter material was filled in to cover the pore pressure gauge until reaching the second design depth for the next pore pressure gauge. Following these steps, the pore pressure gauges were installed at intervals of 3 m and 2 m. Filter material was filled to the design depth, and then the remaining space between the well tube and the borehole wall was backfilled using high-quality clay balls. The pore pressure gauges were positioned outside the wells to monitor the pore pressure in the filter materials. The groundwater pressure head at the observation point can be calculated using Equation (1):  
\[H=\frac{p}{\gamma_{w}} \tag{1}\]  
where \(H\) is the piezometric head (m); \(p\) is the pore pressure (kN); and \(\gamma_{w}\) is the unit weight of water (kN/m\({}^{3}\)). The DT515 automatic data acquisition instrument was used to collect the data during the in-site pumping test. The time interval of data collection was 1 min. It can connect 30 group data simultaneously, and automatically store them in digital text format. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{4}{c}{**Depth of Sampling (m)**} \\ \cline{2-5}
**Parameters** & **Miscellaneous Fill** & **Silt** & **Muddy Soil** & **Gravel** \\  & **1–2** & **2–17** & **17–29** & **>29** \\ \hline \(E_{\text{s}}\), (MPa) & 3 & 8 & 4 & 30 \\ \(V\) & 0.31 & 0.31 & 0.42 & 0.2 \\ \(\gamma\), (kN/m) & 19 & 19.1 & 17.6 & N/A \\ \(K_{\text{v}}\), (m/s) & \(4.0\times 10^{-4}\) & \(7.0\times 10^{-5}\) & \(1.4\times 10^{-7}\) & 0.9 \\ \(K_{\text{h}}\), (m/s) & \(5.0\times 10^{-4}\) & \(8.5\times 10^{-5}\) & \(2.0\times 10^{-7}\) & 0.9 \\ \(E\) & N/A & 0.82 & 1.22 & N/A \\ \hline \hline \end{tabular} Note: E\({}_{\text{s}}\), Compression modulus; \(v\), Poisson ratio; \(\gamma\), Unit weight; K\({}_{\text{v}}\), Vertical hydraulic conductivity; K\({}_{\text{h}}\), Horizontal hydraulic conductivity; \(e\), Void ratio.  
\end{table} 
Table 2: Soil parameters obtained by laboratory and field tests. The piezometric head of an observation point can be calculated by adding the position elevation and the pressure head. Variations in pore pressure before and after dewatering can be observed and calculated as drawdown. As the experimental pumping wells had been adequately flushed and the mud skin was torn off, the pore pressures were observed in the filter material outside the well casing and drain, rather than inside. The drawdown represented the aquifer drawdown near the pumping well rather than the drawdown inside the pumping well. Nonlinear effects occurred when groundwater entered the well pipe through the well casing and drain.