As a result of the siphon phenomenon in soft soil siphon drainage, groundwater is discharged from the soft soil without any power, and this increases the effective stress in the soil. A significant part of the drainage effect is determined by the spacing of the siphon holes. According to the model test presented in this study, the decrease in the groundwater level is more pronounced when the spacing of the siphon holes is smaller. In comparison to the single-hole test, the spacing of 0.4 m is 107.6% larger. Based on subsequent numerical simulations, it has been found that when the hole spacing is reduced to 1.0 m, the decrease in the groundwater level on the 60th day can reach the limit value of 10 m for soft soil with a permeability coefficient of 10−9 m/s. In addition, the field test indicates that the average decrease in the water level of the 0.9 m hole spacing is 75.9% greater than that of 1.8 m, while the time required to reach the same decrease in the water level is 63.6% shorter.

The drainage consolidation method can reduce porosity to consolidate soft soils. In this study, a novel siphon drainage method is used as the drainage consolidation method to lower the groundwater level. Compared to other drainage methods, the siphon drainage method is power-free, environmental-friendly, and highly efficient. Numerical simulations are conducted to verify the feasibility of the siphon drainage method on soft soil treatment. In addition, the effects of soil permeability and drainage hole spacing on its application efficiency have been studied. The results show that: (a) The siphon drainage method can accelerate the consolidation by lowering the groundwater level; (b) The larger the soil permeability is, the faster the pore water pressure decreases; (c) Adopting 1 m hole-spacing in the siphon drainage is much more efficient than methods which have a 2 m hole-spacing. In addition, the siphon drainage method is proven the effective in soft soil foundation treatment by a field test in Zhoushan, Zhejiang Province.

The use of a siphon is a drainage method that does not require the use of external power, and siphons are used extensively in practice. The application of siphons in the treatment of soft soils has become a popular approach in recent years. Analyzing the change in the water level in multi-well siphoning is the basis of the application of siphons. The calculation model of multi-well siphoning is established through equivalent transformation. A finite difference method is used to solve the model, and the accuracy is verified by comparing the results with a test of the model and with field tests. Using the numerical model, the feasibility of siphoning drainage in soft soil is demonstrated from two aspects, i.e., well spacing and the permeability coefficient. The results show both the “minimum drop increase” and the “average drop increase”, as well as the spacing of the decreases or increases in the permeability coefficient. When the permeability coefficient is 1 × 10−8 m/s and the well spacing is 2 m, the decrease in the water level is approximately 9.72 m after 100 days of drainage. It is feasible to apply siphon drainage technology to discharge the groundwater in soft soil.