## 4 Engineering Example Verification  
### Project Overview  
Yangwan Station is situated beneath the north section of Zhongzhou East Road in Luoyang City. It is the terminal station of Luoyang Metro Line 1. The groundwater type of the site is characterized as Quaternary pore phreatic water, which mainly occurs in the sandy pebble layer and has strong permeability. According to the geological survey report relating to Yangwan Station, the groundwater level is located 10 m below the ground surface; the thickness of the aquifer is about 90 m, and the permeability coefficient of the stratum is about 60 m/d. The foundation pit support form of Yangwan Station is a secant pile with internal support. The width of the support structure is 1 m, and the depth of the support structure is 28 m; the thickness of the flow cross-section is 72 m. The total length of the station is 432.3 m, the total width of the standard section of the structure is 20.7 m, and the depth is about 18 m. The layout of the precipitation wells is as follows:  
On 28 April 2018, the dewatering wells in the foundation pit were D1-J7 and D73-79. The water level elevation in the foundation pit at the west end is 8.38 m lower than the initial groundwater level elevation; that is, the water level in the pit is stable at 81.62 m. It can be seen that the depth of the waterproof curtain inserted into the groundwater in the pit is 9.62 m. The results of water yield measurement of precipitation wells are as follows:  
According to Table 1, the total water inflow is 724.9 m\({}^{3}\)/h, while the precipitation length cannot be calculated accurately. Based on the actual prediction of the project, the precipitation length of the D1 precipitation well and the D73 precipitation well on the east side of the pit is the spacing of the two neighboring precipitation wells: 15 m. The total precipitation length is the width of the west end of the pit and the length of the precipitation of the two sides of the pit, as illustrated in Figure 4; the total length of precipitation is about 221.8 m. The water inflow per unit width Q is the ratio of the total water inflow to the total precipitation length:  
\[Q=3.27\text{m}^{3}/\text{m}\cdot\text{h}=78.44\text{m}^{3}/\text{m}\cdot\text {d}, \tag{20}\]  
According to the field-measured data, the water level elevation in the R6 observation well is 4.08 m lower than the initial water level elevation. That is, the water level of the R6 observation well is 85.92 m, and there is still a distance between the R6 observation well and the waterproof curtain of the foundation pit. Therefore, the actual water level outside the curtain will be slightly lower than this value. In the subsequent verification, the reduction in the water level from the observation well to the waterproof curtain is ignored, and the water level outside the curtain is 85.92 m.  
According to the project overview, the values of the parameters in the calculation model are as follows:  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
\begin{tabular}{c} **Dewatering Well** \\ **Number** \\ \end{tabular} & **Water Inflow/m\({}^{3}\)/h** \\ \hline D1 & 67.8 & D73 & 49.7 \\ D2 & 40.7 & D74 & 48.6 \\ D3 & 36.2 & D75 & 31.7 \\ D4 & 63.3 & D76 & 63.0 \\ D5 & 36.3 & D77 & 30.9 \\ D6 & 72.3 & D78 & 49.5 \\ D7 & 85.9 & D79 & 49.0 \\ \hline \hline \end{tabular}
\end{table}
Table 1: The measurement results of the water yield of the operating dewatering wells in Yangwan Station.  
Figure 4: Dewatering well layout of Yangwan Station.