# A Siphon Drainage Method for Consolidation of Soft Soil Foundation
## 4 Field Test of Siphon Drainage in Soft Soil Consolidation
### Field Test in Zhoushan  
Field test is conducted in Zhoushan to study the effects of the siphon drainage method. The test site is selected in a 10 \(\times\) 15 m area. Firstly, the permeable pipes with one end of the siphon pipes in them are inserted into the soil to form siphon drainage holes through the  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Soil**} & **Moisture** & **Wet Density** & **Dry Density** & \multirow{2}{*}{**PORE RATIO**} & & **Vertical** & **Horizontal** & \multirow{2}{*}{**Compressibility**} \\  & **Content (\%)** & **(g/cm\({}^{*}\))** & & **(g/cm\({}^{*}\))** & & **Cofficient** & **Cofficient** & **An\({}_{z}\) (MPa\({}^{-1}\))** \\ \hline stamped soil & 38.9 & 1.81 & 1.31 & 1.13 & 16.2 & \(4.2\times 10^{-7}\) & \(5.78\times 10^{-7}\) & 0.95 \\ gray-yellow & 40.5 & 1.78 & 1.27 & 1.15 & 14.7 & \(2.2\times 10^{-7}\) & \(1.6\times 10^{-7}\) & 1.08 \\ gray silty clay & 41.3 & 1.78 & 1.26 & 1.17 & 15.1 & \(2.2\times 10^{-7}\) & \(1.7\times 10^{-7}\) & 0.87 \\ silty clay & 29.7 & 1.92 & 1.5 & 0.83 & 14.5 & \(1.1\times 10^{-7}\) & \(4.8\times 10^{-7}\) & 0.39 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Summary of geotechnical test results of soil physical properties.  
construction machine (Figure 10a). The average depth of the siphon drainage holes is 18 m. Then put the other end of the siphon pipes into the pump well and start the siphon process (Figure 10b). Automatic control of the pump ensures that the water level in the pump well is always below 15 m, allowing groundwater to flow continuously into the well.  
In order to find the change in groundwater level in the soft soil foundation during the siphon drainage process, water level gauges were placed in some siphon drainage holes. To understand the effect of the siphon drainage method, the surface settlement deformation monitoring and the layered settlement monitoring were carried out on site. The layout of on-site monitoring holes and monitoring points is shown in Figure 11.  
Figure 11: Layout of monitoring holes and points.  
Figure 10: The figures of field test. (**a**) Construction of siphon drainage holes. (**b**) Top view of field test.  
In order to verify the consistency between the numerical model and the field test results, a numerical model was established with nine siphon drainage holes as the unit based on the field geological condition. The horizontal direction of the model is a rectangle with a side length of 2.7 m, and the siphon drainage holes are distributed in a rectangular manner with a spacing of 0.9 m. According to the results of the geotechnical test, the vertical depth of the model is set to 22 m (see Figure 12). In addition, it is divided into 11 layers. The soil parameters of each layer are shown in Table 2. The siphon drainage holes are drilled at a depth of 18 m. When draining water, the surrounding eight siphon pipes are working. The central well is a groundwater level monitoring hole. The surface settlement monitoring point is located between two siphon drainage holes, which is consistent with the field test. The rest of the condition settings are the same as above.