A New Method For Simultaneous Measurement Of Soil-Water Characteristic Curve And Permeability Coefficient For Unsaturated Soils

The permeability coefficient of unsaturated soil is an important parameter to analyze the stability of rainfall on soil slope,solid waste landfill,underground sewage migration and landfill engineering.Due to the presence of matrix suction in unsaturated soils,the permeability coefficient cannot be determined by conventional permeability test methods,making it difficult to determine the permeability coefficient of unsaturated soil.This paper conducts a comprehensive study on the permeability characteristics of Hunan red clay at different dry densities through specific experiments and theoretical analysis.An improved pressure plate instrument is used to carry out the unsaturated soil permeability test.The new method of permeability coefficient and soil-water characteristic curve was verified by using the measured data of pressure plate instrument and the prediction model of unsaturated permeability coefficient.The prediction model of air-entry value is used to predict the air-entry value of deformed soil.The specific research contents are as follows:(1)The seepage flow of unsaturated soil is introduced in detail,the concept and composition of soil water potential in unsaturated soil are expounded,and several different suction measurement methods are also listed,their application scope and advantages and disadvantages are introduced,the application of axial translation technique in the adsorption force test of unsaturated soil is emphasized,then the capillary action is described,from the surface tension to the formation of capillary phenomena and the hydrostatic balance of capillary action,and finally the concept of Darcy's law,the scope of application of Darcy's law and its promotion and applications in unsaturated soils(2)The soil-water characteristic curve was tested by pressure plate instrument,and three groups of dry density of soil samples were selected to obtain more accurate and effective soil-water characteristic curve,so as to analyze the actual engineering application.Based on the analysis of soil-water characteristic curve by three SWCC models,the advantages and disadvantages of the model and its application range are discussed.At the same time,the variable water head permeability meter was used to obtain the saturation permeability coefficients corresponding to different dry densities.(3)This paper proposes a measurement method based on the simultaneous measurement of unsaturated permeability coefficient and soil-water characteristic curve based on axis translation technology.In order to meet the measurement needs of the experiment,the instrumental device of the soil-water characteristic curve pressure plate instrument was modified to increase the accuracy of the instrument and the simultaneous measurement of the unsaturated permeability coefficient test and the soil-water characteristic curve test of the Hunan clay with the modified test device.Because the test takes a long time,this paper selects three dry densities of Hunan clay samples to obtain the change of unsaturated permeability coefficient in the range of0?200kpa,and draw a regular curve to analyze the test results.(4)Select the appropriate unsaturated permeability coefficient model to predict the unsaturated permeability coefficient,and compare the predicted result with the measured value of the unsaturated permeability coefficient.At the same time,a prediction model for the air-entry value of deformed soil is proposed,and the measured data is used to verify the reliability of the prediction model in this paper.