Simulation Study Of Siphon Drainage Effect In Soft Soil And Its Application Test Analysis

Soft soil,which is characterized by high compressibility,large water content,poor permeability,and low strength,is widely distributed in China.The most common method for strengthening a soft soil foundation is via the drainage consolidation method Among the existing drainage consolidation methods,the surcharge preloading method requires a large number of heavy materials and is time-consuming and labor-intensive.Moreover,the vacuum preloading method has high energy demands.As such,exploring an economical and environmentally friendly new drainage consolidation method is an important research topic in the field of soft soil foundation treatment.The siphon phenomenon is caused by molecular gravity and potential energy difference and has the characteristic of achieving water transfer without power.It is also an environmentally friendly,economical,convenient,and effective drainage measure.The siphon drainage technology has been well applied in the treatment of rainfall-induced landslides,and its application in the drainage of soft soil water is a new research direction.Analyzing the variation process of groundwater levels under siphon drainage is the foundation for a soft soil siphon application.Therefore,corresponding research has been conducted from three aspects: theoretical calculation;model testing;and on-site application testing.(1)A calculation model for group hole siphon drainage was established based on the symmetrical distribution of groundwater level.The model’s accuracy was verified by comparing the model’s numerical solution with the experimental results of the physical model.Compared with the Jacob single-well model,which is also a fixed-depth well-flow problem,the group hole siphon drainage calculation model is more suitable for calculating groundwater levels under group hole drainage conditions in practical engineering.(2)Based on the Neuman model,a soft soil siphon drainage calculation model considering the influence of vertical seepage was established.Comparing the calculated results of the model with the numerical simulation results shows that the accuracy of the model is improved compared with when vertical seepage is not considered.After considering the influence of vertical seepage,there will be differences in the height of water head under siphon drainage in the vertical direction.The larger the vertical distance from the bottom of the drainage hole,the higher the corresponding water head height.As the drainage time increases,the head height difference at different vertical distances from the bottom of the drainage hole also increases accordingly.(3)The influence of water level drop of the drainage hole and hole spacing on siphon drainage was studied through physical model experiments and numerical simulation methods.The physical model test results show that,when the water level drop of the drainage hole increases from 15 to 35 cm,the minimum water level drop increases by 80.0%;when the hole spacing decreased from 100 to 40 cm,the minimum water level drop increased by 57.5%.The numerical simulation results show that,as the water level drop of the drainage hole increases,the water level drop increases proportionally,and the two show a linear relationship.As the hole spacing decreases,the water level drop first slowly increases then rapidly increases,and the two show an exponential relationship.(4)Through on-site application testing of siphon drainage,systematic monitoring of groundwater level and soil deformation is conducted to demonstrate the feasibility of soft soil siphon drainage technology in practical engineering.The test results show that the water level drop of the drainage hole has remained stable for a long time at over 9.6 m,resulting in an average groundwater level drop of 5.18 m and an average surface settlement of 411.5 mm.After the test,the average moisture content of the soil decreased by 15.8% and the average compressive modulus increased by 32.5%.This indicates that siphon drainage has strong stability,which can effectively reduce groundwater levels,accelerate compression and consolidation of soft soil,and improve the physical and mechanical properties of soft soil.(5)Compare the reinforcement mechanism between siphon drainage and vacuum preloading.The effective stress increment of soil under siphon drainage gradually increases with the increase of depth and finally remains at a fixed size.The effective stress increment of soil under vacuum preloading gradually decreases with the increase of depth and finally decreases to 0.This indicates that siphon drainage is more suitable for the reinforcement treatment of deep soft soil,while vacuum preloading is suitable for the reinforcement treatment of shallow soft soil.