## 3 Field Experiments
### YB8 Pumping Test  
Figure 8 presents the relative spatial positions of the diaphragm wall, the pumping well, and the observation well. Pumping well YB8 was installed in the middle of Pit B's long side, flanked by a waterproof curtain on both sides. The shortest distance from the diaphragm wall was 4.89 m. Observation well YB3 was positioned at the corner of the pit wall, 4.5 m from the diaphragm wall, 14.42 m from the sealing wall, and 38.05 m from the pumping well. Another observation well, YW1, was located outside the pit, 1.01 m away from the diaphragm wall and 6.9 m away from the pumping well. In the vertical section, the filter tube of the pumping well was encased within the wall by 11 m.  
Figure 6: Drawdown profile of the three wells in the first dewatering. Figure 8: Spatial relative positions of the diaphragm walls, the drainage well, and the observation wells for the YB8 test: (**a**) Top view; (**b**) Section view. Figure 7: Hydraulic gradient between the drainage well (i.e., YA17) and observation well (i.e., YA19 and H2) profiles in the first dewatering. Figure 9 shows the drawdown at various depths of well YB8 during the two-round pumping test. In the first round of pumping, the pump rate reached 60 m\({}^{3}\)/h, whereas in the second round, the pump rate decreased to 35 m\({}^{3}\)/h. Initially, the drawdown at all monitoring points increased sharply and later stabilized during the first round. The maximum drawdown reached 27 m, equivalent to the maximum drawdown of 25 m observed in the YA17 test, as the filter thickness of YB8 was shorter than that of YA17. The maximum drawdown was located near the filter's bottom, mirroring the results from the YA17 test. During the second round of pumping, the reduction in the pump rate did not affect the location of the maximum drawdown (still near the bottom of the filter). However, due to the pump rate reduction, the drawdown at all monitoring points decreased. After the cessation of pumping, the water level swiftly returned to its initial state. Figure 10 displays the drawdown distributions at different depths for wells YB8, YB3, and YW1 during the initial dewatering. The drawdown of well YB8 closely matched that of well YB3 for burial depths less than 35 m (above the filter). The drawdown of well YB8 then increased with burial depth, peaking at 46 m. Conversely, the drawdown of observation well YB3 decreased with increasing burial depth and remained constant below the bottom of the diaphragm wall. Figure 9: The drawdown at different depths of well YB8 in the two steps: (**a**) first dewatering; (**b**) second dewatering and recovery stage. The maximum drawdown of pumping well YB8 was similar to that observed in the YA17 test. However, the maximum drawdown of observation well YB3 within the pit was 12 m, larger than the drawdown of observation well YA19 in the YA17 test due to the higher pump rate in the YB8 test. Moreover, the drawdown in the observation well YW1 was nearly zero, attributable to the blocking effect of the unclosed diaphragm wall. This result demonstrates that an unclosed diaphragm wall can effectively prevent groundwater reduction outside the foundation pit. During construction, the large drawdown obtained in the pit can lower the groundwater level with higher efficiency, which can be referred to by similar engineering. In urban planning, the excavation and dewatering of the foundation pit of a new project have to be controlled to protect the existing buildings in a built-up area. The small drawdown obtained outside the pit can protect the nearby urban environment. The practical utilization of the effect can increase the bearing capacity of underground space and enlarge the exploitable land area. A 3D groundwater flow pattern can be artificially formed by designing proper diaphragm walls and pumping wells. A retaining structure-dewatering coupling design procedure and method can be developed to utilize the diaphragm wall-pumping wells coupling effect.