# A Siphon Drainage Method for Consolidation of Soft Soil Foundation
## 5 Conclusions  
The drainage consolidation method is widely applied to strengthen the soft soil foundation. However, with respect to the thick foundation, the traditional drainage consolidation method tends to be less effective for the soils in the deep. It would be beneficial for the drainage consolidation method to combine with methods lowering the groundwater.  
The siphon drainage method is a power-free and easy-operated method to lower the groundwater level at a certain depth below the soil surface. By artificially setting the height difference in the groundwater level, this method utilizes the principle of siphon without power to achieve efficient drainage of large areas of low-permeability soft soil. As a result, the buoyant weight of soils over the flow profile is changed to natural weight, which makes the preloading of the drainage consolidation method more efficient.  
Numerical simulations were conducted and validated the feasibility of the siphon drainage method in the soft soil treatment. In addition, its rationality was verified by comparing with the field test results. Moreover, the influence of soil permeability and drain hole spacing is studied. The results show that: (a) When the drain hole spacing is the same, the larger the soil permeability is, the faster the drop rate of pore pressure is. (b) When the soil permeability is the same, the smaller the drain hole spacing is, the faster the drop rate of pore pressure is. (c) The process of drainage has a lag time in the bottom of the soil. (d) By comparing with the test results, the trend reflected by the numerical model has a high degree of fitting with the actual situation, and it can be applied to the prediction in actual engineering.  
The field test was conducted in Zhoushan. The test results show that: (a) The groundwater level drawdown in drainage holes reached more than 9 m, which was close to the limit lift of the siphon. (b) The deformation rate of the subsidence on the soil surface was relatively fast in the initial stage, and then became stable in a constant velocity during  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Days**} & \multicolumn{8}{c}{**Magnetic Ring**} \\ \cline{2-7}  & **01** & **02** & **03** & **04** & **05** & **06** & **07** \\ \hline
24 December 2021 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\
28 December 2021 & \(-19\) & \(-19\) & \(-17\) & \(-15\) & \(-8\) & 1 & 10 \\
30 December 2021 & \(-33\) & \(-34\) & \(-31\) & \(-22\) & \(-17\) & \(-1\) & 12 \\
3 January 2022 & \(-81\) & \(-85\) & \(-82\) & \(-71\) & \(-59\) & \(-35\) & \(-15\) \\
7 January 2022 & \(-117\) & \(-123\) & \(-119\) & \(-102\) & \(-88\) & \(-60\) & \(-33\) \\
9 January 2022 & \(-148\) & \(-152\) & \(-148\) & \(-125\) & \(-111\) & \(-77\) & \(-48\) \\
12 January 2022 & \(-158\) & \(-161\) & \(-157\) & \(-131\) & \(-119\) & \(-80\) & \(-51\) \\
15 January 2022 & \(-198\) & \(-200\) & \(-189\) & \(-158\) & \(-142\) & \(-102\) & \(-68\) \\
18 January 2022 & \(-236\) & \(-232\) & \(-219\) & \(-187\) & \(-169\) & \(-123\) & \(-88\) \\ \hline \hline \end{tabular}
\end{table}
Table 3: Layer sedimentation monitoring results (unit: mm).  
siphon drainage. (c) From surface to bottom, the deformation decreased. The siphon drainage not only produced compressive deformation in the groundwater level drop area, but also produced compressive deformation below the groundwater level.  
Conceptualization, methodology, J.Z.; software, validation, S.Y.; formal analysis, investigation, Q.S.; resources, data curation X.W.; writing--original draft preparation, J.W.; writing--review and editing, H.S.; visualization, supervision, J.S. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Natural Science Foundation of China Key Project (No.42230702).  
Not applicable.  
The authors declare no conflict of interest.