Abstract: Soft soil has the characteristics of poor permeability and low bearing capacity. The treatment of soft soil foundation is always a major problem in geotechnical engineering. With the characteristics of free power in drainage, the siphon drainage method can be applied in soft ground the treatment to improve the properties of the soil. Based on the discretized Theis well flow model and the nonlinear layered summation method of settlement, this paper constructs a water level and settlement calculation model considering the changes in permeability coefficient and compressive modulus by settlement with porosity as the core for the unique fixed-deck precipitation model of the siphon drainage method. The effect of the siphon drainage method in soft foundation treatment is analyzed from the aspects of soil permeability coefficient, drainage board spacing, and site size. The results mainly focus on the following three aspects. First, the calculation outcomes are compared with numerical simulation results and the reliability of the calculation model is verified. And the siphon drainage method can perform well in drainage and consolidation for soils of different permeability coefficients in Zhejiang coastal areas. Second, adjusting the spacing of drainage plates can significantly control the drainage consolidation time and the groundwater level. Third, the additional stress caused by drainage will extend into the soil as the site area increases, and for a 50 m×50 m site, the effective influence depth can reach 27.31 m below the surface, which is far beyond the limit of siphon lift. Therefore, the siphon drainage method will get a better effect in practical large-area soft soil foundation treatment.

Key words: soft soil, siphon drainage, foundation settlement, unsteady flow, well group interference