Experimental Study On Unsaturated Permeability Coefficient Of Soil Hygrscopicity And Dehumidification

In engineering practice,it can be considered that the soil above capillary saturation zone is in unsaturated state.When the soil is exposed to rainfall or natural evaporation,the water content in the soil will change repeatedly between the saturated water content and the air-dried water content.In this process,both the soil-water characteristic curve and the permeability coefficient curve show hysteretic characteristics,that is,under the same soil suction value,the soil moisture content and permeability coefficient are not unique.Accurate determination of unsaturated permeability coefficient curve is of great significance to the evaluation of slope stability and the calculation and Simulation of pollutant transport and storage in soil.The unsaturated permeability coefficients of six kinds of soils(sand and silt)in the process of hygroscopicity(capillary rise and vertical infiltration)were measured by wetting front advance method through unit tests in laboratory.The similarities and differences of the unsaturated permeability coefficients measured in different hygroscopicity processes were compared and analyzed.The unsaturated permeability coefficients of six kinds of soils during dehumidification(evaporation)were measured by transient profile method.The unsaturated permeability coefficient of soil is calculated by improving the transient profile method,introducing the parameters of weight change in evaporation process and combining with the matrix suction.The new method is compared with the results of moisture content method,and the way to improve the method is put forward again,which provides a new idea for calculating the unsaturated permeability coefficient of soil in the process of dehumidification by the transient profile method.Through the analysis of the experimental data and the principle of the method,It is found that the main difference between the two methods is that different calculation methods are used to measure the flow through the section.When the two measured profiles are close,two methods can be used to process the same set of experimental data.Evaporation tests were carried out on six kinds of experimental soils to simulate the process of soil drying and dehumidification,and the unsaturated permeability coefficient of soil in the process of dehumidification was calculated by transient profile method.The soil-water characteristic curves of six kinds of soils in the process of dehumidification and hygroscopicity were measured by unsaturated consolidation instrument under the condition of k0.The hysteresis phenomenon of soil-water characteristic curves in the process of dehumidification and hygroscopicity was verified.At the same time,the unsaturated permeability coefficient curves of six kinds of soil samples were obtained by using Van Genuchten-Burdine model,and the hysteresis phenomena of unsaturated permeability coefficient in the process of desorption and hygroscopication were analyzed.