## 3 Field Experiments
### Diaphrag Wall-Pumping Well Coupling Effect Analysis  
The seepage mode near waterproof curtains can be classified into three types based on balancing the dewatering in a deep foundation pit and the drawdown outside of the pit using waterproof curtains: (1) closed waterproof curtain seepage mode; (2) phreatic unclosed waterproof curtain seepage mode, and (3) confined unclosed waterproof curtain seepage mode. The third mode was employed in the dewatering of this foundation pit. The aforementioned tests demonstrated that groundwater assumes a 3D flow state during dewatering and is closely related to the wall-well effect. (1) The curtain serves as a barrier, preventing groundwater from entering the filter directly along the horizontal direction. Instead, the groundwater must navigate through the curtain using a 3D flow, moving vertically initially and then horizontally into the filter. As evidenced by the tests, when the pumping well maintained a nearly constant drawdown inside the pit, the drawdown outside the pit remained less than 0.45 m at all times and did not influence the external drawdown. The relative decrease in hydraulic conductivity helped to minimize the flow in the 3D direction around the vertical flow. In addition, maintaining the foundation pit at a constant drawdown adhered to [PERSON]'s principle of unsteady seepage. As a result, disturbances to the environment outside the pit during the dewatering process were minimal. (2) According to the tests, the maximum drawdown in the pit during the first round of pumping for YA17 exceeded 25 m, with a pumping rate of 35 m\({}^{3}\)/h. However, the theoretically calculated pumping rate for dewatering without a waterproof curtain was significantly larger than that in the YA17 test. This is because the shortest path of underground seepage in the pit would increase (i.e., twice the distance from the top of the filter to the bottom of the wall) when the water head difference remained constant, which is consistent with [PERSON]'s law. Additionally, having the diaphragm wall penetrate to a certain depth into the gravel-confined aquifer reduced the cross-sectional area. Given certain conditions of the water head difference between the interior and exterior of the pit, as well as hydraulic conductivity, reducing the discharge flow cross-section decreased the flow of water, in accordance with [PERSON]'s law. As a result, an unclosed waterproof curtain could decrease the water flow, thereby saving time and money by reducing the need for additional pumping wells. The observed results confirmed the physical model tests [46], numerical simulations [8; 35; 47], and hydrogeological theories [48], which anchored the current study within the broader scientific context. Further studies were necessary to connect the observed results with theoretical analysis. Figure 11: The hydraulic gradient between the drainage well (i.e., YB8) and observation (i.e., YB3 and YW1) in the first dewatering. (3) The natural hydro-geological conditions of pumping tests conducted in Pit A and Pit B were similar. However, the position of the pumping well corresponding to the diaphragm wall was different. The YA 17 was installed close to a middle cut-off wall. The aquifer was also cut off in that direction. The aquifer was partially cut off in three directions for the YB17. The YB 8 was installed far from the middle cut-off wall. The aquifer was partially cut off in two directions for the YB8. The 3D flow effect of YA17 was more obvious than that of YB8 for pumping wells. The drawdown in YA17 reached the maximum value with the help of the side cut-off boundary. A large drawdown was reached nearby pumping well above the diaphragm wall bottom, and a small drawdown downwards below the bottom of the diaphragm wall was observed, indicating that a perfect 3D diaphragm wall-pumping well effect was reached. The drawdown of YB8 also reached the maximum value with the help of the diaphragm wall.