## 2 Overview of the Engineering  
The foundation pit of the No. 4 working shaft of the Guanyuan project in the Pudong New Area of Shanghai was selected as the background. The foundation pit is located at Jihui Road, 97.1 m away from the West 220 kV high voltage tower, 12 m away from the east substation, and 8.5 m away from the pump house (Figure 0(a)). The size of the foundation pit is 55 m \(\times\) 50 m, the ground elevation is 4.5 m, the excavation depth is 39.6 m. The foundation pit bottom is located in the silty clay of layer \(\circledR\). The retaining system includes a diaphragm wall and a trench-cutting remixing deep wall, together with internal support. Dewatering, drainage, and water proof measures are adopted to control ground water. The surrounding environment of the foundation pit is complex and the dewatering subsidence has to be strictly controlled. The soil layer within 150 m depth of the site is composed of Quaternary Holocene to middle Pleistocene sedimentary strata. The strata are divided into 13 main engineering geological layers (Figure 0(b)):layers \(\circledD\), layer \(\circledR\), layer \(\circledR\), layer \(\circledR\), layer \(\circledR\), layer \(\circledR\), layer \(\circledR\) (clayey silt with silty clay), layer \(\circledR\) (silty clay), layer \(\circledR\) (sandy silt), layer \(\circledR\) (silty clay and silt), layer \(\circledR\) (silty sand with silty clay), layer \(\circledR\) (silt), and layer (11) (silt). The aquifers consist of a phreatic aquifer (shallow soil layers), a slightly confined aquifer (layer \(\circledR\)) confined aquifer I (layer \(\circledR\)), confined aquifer II (layer \(\circledR\)), and confined aquifer III (layer (11)). The stratum distribution and groundwater situation are shown in Figure 0(b), and the corresponding parameters are shown in Figure 0(a). The water level of confined aquifer layer \(\circledR\) is \(-1.40\) to \(-2.64\) m; the water level of confined aquifer layer (b) is \(-1.00\) m; the water level of confined aquifer layer (11) is \(-2.15\) m. The anti-gushing calculation of confined water and safe drawdown of layers (b), (b)\({}_{21}\), (b), and (11), according to the above water level, is shown in Table 1.  
Figure 1: Layout of the No. 4 working shaft, Guangyuan project, Shanghai China: (**a**) No. 4 working shaft; (**b**) Hydrogeological profiles.  
Figure 2: Soil parameters of the No. 4 working shaft, Guangyuan project, Shanghai China. Note: \(\gamma\) = unit weight; \(w_{n}\) = water content; \(w_{p}\) = plastic limit; \(w_{L}\) = liquid limit; \(e\) = void ratio; \(a_{1,0-0.2}\) = coeffient of compressibility; \(c\) = cohesion; \(\varphi\) = internal friction angle.  
The normal depth of a traditional horizontal waterproof curtain is approximately 50 m to 70 m, although the maximum depth of the diaphragm wall has reached 150 m, forming a horizontal curtain in the aquifer when the depth exceeded 70 m in Shanghai. The materials used in a traditional horizontal waterproof curtain-forming method are mainly cement and lime cementitious materials, which may cause adverse effects on the ecological environment of groundwater. Traditional grouting materials cannot enter the deep sand layer with small pores without destroying the soil structure.