Research On The Permeability Characteristics Of Unsaturated Soils With Different Initial Void Ratios

Unsaturated soil is the soil which is filled with water and air at the same time,and its saturation is less than 100%,it is the most widely distributed soil on the earth's surface,and is often encountered in practical engineering.Many problems are related to the permeability characteristics of unsaturated soils,such as natural slope's failure after continuous rainfall,migration process of underground pollutants in landfill,consolidation of compacted soil in the foundation or roadbed and swell of expansive soil.Soil water characteristic curve and permeability coefficient are the key parameters to evaluate the permeability characteristics of unsaturated soil.The soil water characteristic curve can reflect the pore structure characteristics and water holding capacity of unsaturated soil,there are many methods for its testing at present,and choosing the appropriate model to fit the test data is an important work.The permeability coefficient is the key parameter to measure the water flow capacity of unsaturated soil,and its value varies greatly and is difficult to measure,it has been a difficult point in the study of unsaturated soil.In this paper,the permeability characteristics of Hunan clay with different initial void ratios are studied by means of the specific experiments and theoretical analysis,and the variation law of soil permeability characteristics under compression deformation has also been studied.The main research contents are:(1)The characteristics of shrinkage film as independent phase in unsaturated soil,and the formation and expression of surface tension are introduced,the composition of soil water potential and the definition and measurement of matric suction are analyzed.The application of Darcy's law in unsaturated soil is introduced,and we measured the saturated permeability coefficient by using variable head test.(2)By using pressure plate apparatus,the soil water characteristic curves of Hunan clay samples with different initial void ratios are obtained.comparing various classical models of soil water characteristic curves,and combing with the test data,we used Matlab,Origin and other software for fitting analysis,pointed out the advantages and disadvantages of each model and their applicability,and selected the optimal model for the follow-up study.(3)According to the measuring methods of the permeability coefficient of unsaturated soil,we made organic glass barrel device for transient profile test,measured the water content profiles of soil columns with different initial void ratios in one-dimensional seepage state,got the seepage velocity and average hydraulic gradient by using the differential calculation of different sections of soil columns,thus calculat ed the unsaturated permeability coefficient finally.(4)The indirect prediction models of permeability coefficient of unsaturated soil are introduced.By using the soil water characteristic curve prediction method,the Childs and Collis-George correction model and the Tao hole model are chosen respectively to predict the permeability coefficients,we compared and analyzed the predicted values and the measured values,and obtained some relevant conclusions.