# A Siphon Drainage Method for Consolidation of Soft Soil Foundation
###### Abstract  
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. soft soil; siphon drainage; consolidation; groundwater level; pore water pressure +
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the surface areas. However, this method is time-consuming and labor-intensive with less efficiency. For well point drainage, the major measurement is to use well holes to pump the groundwater in the foundation. There are several types of well point drainage, for example, light well point drainage, jet well point drainage, tube well point drainage, electroosmotic well point drainage, etc. [19]. With respect to soft soils, the low permeability (usually less than \(10^{-6}\) cm/s) makes the above measurements less applicable except for electro-osmotic well point drainage. However, due to the high cost of both economy and energy, the electro-osmotic well point drainage is not well adopted. Therefore, developing a time-efficient and cost-efficient manner to lower the groundwater level in soft soil foundations provides great value in engineering construction. The siphon phenomenon is an ancient discovery, which is caused by the molecular gravity of the molecules of a liquid and different potential energy [20]. It is often used for drainage of slopes with large permeability coefficients [21; 22]. As reported in the previously published literature, a drainage method based on the siphon phenomenon has been developed and has achieved excellent results in many landslide control projects. [PERSON] [23; 24] designed an automatic siphon drainage system for slopes, in a patent, with 10-30 mm diameter pipes. The team of [PERSON] [25; 26] concentrated on the application of millimeter siphon pipe diameters for potential landslide water table precipitation. Siphon drainage is usually applied to soil with a large permeability coefficient. The corresponding research is required to verify whether the siphon drainage is applicable to soft soil with low permeability. Some scholars have carried out physical simulation tests in the early stage to examine the feasibility of siphon drainage technology in soft soil foundation [27; 28]. However, these studies only stay at the stage of the small-scale model test, and there is still a lack of large-scale field tests and verification. In the traditional application (such as landslides) of siphon drainage, (a) the drainage is usually continuous (the drainage time can last several hours or even several days at a time), and (b) there exists terrain with a natural elevation difference. The application of the siphon drainage method in soil with a large permeability coefficient has achieved good results [29; 30]. It can quickly collect and discharge the water in the soil, effectively lower the groundwater level, and improve the stability of the slope. However, in the application to a large-area of soft soil foundation, (a) due to low permeability, the drainage is intermittent (the drainage time can usually last several minutes at a time), and (b) there is no terrain with a natural elevation difference.