## 4 Analysis on the Impact of Confined Water Approaching Construction on the Existing Station
### Effect of Confined Water on the Deformation of the Existing Station  
Three construction conditions are supposed to analyze the influence of confined water on the existing station.  
Condition I: consider phreatic water (II), interlayer phreatic water--confined water (III), confined water (IV) and confined water (V);  
Condition II: consider phreatic water (II), interlayer phreatic water--confined water (III), confined water (IV), confined water (V) and confined water (VI);  
Condition III: consider phreatic water (II), interlayer phreatic water-confined water (III), confined water (IV), confined water (VI) and confined water (VII).  
30 measuring points are selected at the bottom of the south wall for analysis, and the deformation curve of the existing station is shown in Figure 5.  
As can be seen from Figure 5, the upward deformation caused by confined water increases the structure deformation of the three construction conditions. The deformation led by excavation is 1.89 mm, and the deformation caused by confined water (V) and above groundwater is 2.76 mm, the deformation caused by confined water (VI) is 2.07 mm, and that led by confined water (VII) is 2.94 mm. Groundwater is the major reason for the  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Number**} & \multirow{2}{*}{**Aquifer Type**} & \multirow{2}{*}{**Water Storage Rate \(S_{\text{s}}/\text{m}^{-1}\)**} & **Horizontal Permeability** & **Vertical Permeability** \\  & & & **Coefficient \(K_{\text{s}}/\text{m}\cdot\text{d}^{-1}\)** & **Coefficient \(K_{\text{s}}/\text{m}\cdot\text{d}^{-1}\)** \\ \hline
1 & Diving & 2.356 \(\times\) 10\({}^{-4}\) & 0.003 & 0.002 \\
2 & Diving-Confined water & & 6.495 \(\times\) 10\({}^{-5}\) & 1.31 & 1.62 \\
3 & Aquitard & 1.369 \(\times\) 10\({}^{-4}\) & 0.005 & 0.002 \\
4 & Confined water (IV) & 7.513 \(\times\) 10\({}^{-5}\) & 3 & 1 \\
5 & Aquitard & 1.986 \(\times\) 10\({}^{-4}\) & 0.0004 & 0.002 \\
6 & Confined water (V) & 6.927 \(\times\) 10\({}^{-5}\) & 2.32 & 1.57 \\
7 & Aquitard & 2.013 \(\times\) 10\({}^{-4}\) & 0.0005 & 0.0002 \\
8 & Confined water (VI) & 8.581 \(\times\) 10\({}^{-5}\) & 2 & 1 \\
9 & Aquitard & 2.136 \(\times\) 10\({}^{-4}\) & 0.0001 & 0.0002 \\
10 & Confined water (VII) & 8.627 \(\times\) 10\({}^{-5}\) & 2.24 & 1.42 \\
11 & Aquitard & 2.014 \(\times\) 10\({}^{-4}\) & 0.0002 & 0.0003 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Calculating model main geotechnical parameters table.  
Figure 5: Deformation curve of existing station.  
floating deformation of the existing station. Foundation pit excavation breaks the relative balance between the upper soil and the confined water top force. Under the action of the confined water top force, the formation is constantly upward, resulting in the floating of the existing station, in which the confined water (VI) and confined water (VII) exert a great impact on the station.  
The existence of multi-layer pressure aquifer is the main cause of the floating structure. Since the groundwater is only drained in the pit, the existing structure outside the pit is still affected by the multi-layer confined water top support force, so that the existing structure appears seriously floating after the excavation of the foundation pit. The maximum up floating point cumulative floating curve is indicated in Figure 6.  
As shown in Figure 6, with the occurrence of confined water (VI) and confined water (VII), the bearing force of existing stations ascends, so the floating value and floating rate increase after earthwork excavation; in the process of soil excavation, the unloading effect of the third layer and the fourth layer is remarkable, thus the structure floating is larger.