Study On Drainage Effect Of Unsaturated Soil Subgrade Under Electroosmosis

For railway in operation period,the moisture content of roadbed is easily increased due to the change of external rainfall,groundwater and train load,which affects the engineering properties of roadbed soil.Electroosmosis is a technique of applying direct current to soil,forcing water to migrate from anode to cathode,and discharging from cathode to achieve soil consolidation.In fine grained soil,the water flow caused by current is much higher than that caused by hydraulic gradient,which makes it more advantageous in treating subgrade fill with low permeability compared with conventional drainage measures.Therefore,this thesis aims to apply electroosmosis method to the drainage of railway unsaturated soil subgrade during the operation period.The clay filler with poor natural drainage effect and frost heave sensitivity is taken as the research object.A self-designed electroosmotic test device was used to carry out laboratory tests to study the changes of soil moisture field and electric field and the influencing factors.Based on Darcy’s law,electric seepage equation,fluid mass conservation equation,and the relation between electric permeability coefficient and water content of unsaturated soil,the two-dimensional electroosmotic drainage theory of unsaturated clay is deduced.The main research contents and achievements of this thesis are as follows:(1)A set of laboratory electroosmotic test equipment was designed to carry out one-dimensional electroosmotic drainage test on unsaturated clay,to explore the influence of different initial water content,potential gradient and compactness on the electroosmotic effect.In the process of electroosmosis,the water content,potential distribution,current and other data of soil in different positions were monitored and recorded,and the change rule was analyzed.The interface resistance,energy consumption coefficient and other parameters were calculated to evaluate the electroosmosis effect.(2)Based on the electroosmotic test of subgrade model,the influence of different electrode embedment methods on the electroosmotic effect is studied.It is found that compared with vertical embedding electrodes,when horizontal embedding electrodes are used to achieve vertical drainage of subgrade,the soil moisture reduction effect is better,which is more appropriate to the engineering practice.(3)Based on the linear superposition of hydraulic flow and electroseepage in electroosmotic drainage theory,the fluid mass conservation equation,considering the nonlinear variation of hydraulic permeability coefficient and electric permeability coefficient of unsaturated soil with water content,the two-dimensional electroosmotic drainage theory of unsaturated clay is deduced,the analytical solutions of pore water pressure and water content are obtained,which are compared with the experimental results,and the rationality of the analytical solutions is proved.(4)The parameters of the derived two-dimensional electroosmotic drainage equation are analyzed.By using the control variable method,the effects of such parameters as the ratio of saturated electric permeability coefficient and saturated hydraulic permeability coefficient of soil,the reduction coefficient of V-G model and the difference between saturated volume water content and residual volume water content on the changes of soil pore water pressure and volume water content were explored,providing theoretical support for the design of unsaturated soil electroosmotic drainage.