Moisture Redistribution In The Unsaturated Soil Subjected To DC Electric Field

Water migration in unsaturated soil is mainly driven by matric potential and gravity potential.With respect to an earthen site in moist circumstances,it is the moisture content fluctuation and water migration involved with capillarity that lead to the deterioration of the heritage,such as dry shrinkage and salt weathering.This thesis studies the mechanism that applying direct current field to control capillary water rise in soil.So to investigate the feasibility of conserve a heritage with DC in moist circumstances.Primarily,this thesis analyzed the energy state,and established a theoretical model,describing the moisture redistribution in unsaturated soil subjected by DC electric field,based on Darcy's law,Ohm's law,law of conservation of charge and law of conservation of mass.Furthermore,the relevant parameters included in this model were discussed in detail,such as electrical conductivity,unsaturated permeability coefficient and matric suction to be responsible to soil moisture content.Both the results between laboratory test and theoretical calculation have been compared to verify the reliability of the moisture redistribution model in unsaturated soil.The soil-water characteristic curve(SWCC)and the unsaturated infiltration coefficient were measured to obtain the parameters required for the theoretical calculation.And initial and boundary conditions were set up following the laboratory test conditions for the theoretical calculation.This thesis discussed,the relationship between capillary water and the deterioration of the soil site so to highlight the principle that heritage site can be protected by applying DC to restrain capillary rise.Research results prove that earthen site deterioration is attributed to moisture content fluctuation and salt migration rather than water itself.Therefore,DC electric field can be applied to restrain capillary migration generated by soil matrix potential.The study found that the theoretical model,the moisture redistribution model in unsaturated soil,were in good agreement with the laboratory test data,which can be used to describe quantificationally the effect of DC field on the migration of capillary water.This study tends to support such a conclusion that effective reduction of water content can be achieve by using DC electric field,which,in turn,to protect earthen heritage site by reducing the wet swelling,drying shrinkage and salt dissolution-andcrystallization.