Research On The Relationship Between Fractal Characteristics Of Soil Particle Size And Hydraulic Properties For Unsaturated Soils

The major obstacles to the theoretical study on hydraulic properties of unsaturated soils is the low accuracy and time-consuming measurement of the related parameters in unsaturated soils.This study focuses on the determination of hydraulic properties of unsaturated soils(i.e.,soil-water characteristic curve and hydraulic conductivity function)with the fractal characteristics of particles as a clue.The soil-water characteristic curve is described by the relationship between matrix suction and water content.The hydraulic conductivity function is described by the relationship between hydraulic conductivity and water content or matric suction.Based on the previous theoretical achievements,this paper describes the research progress,characteristics and applications of soil-water characteristic curve and hydraulic conductivity,and summarizes the experimental and theoretical methods for obtaining unsaturated soil-water characteristic curve and hydraulic conductivity.The soil-water characteristic curve and hydraulic conductivity of unsaturated soil is also carried out in experimental investigations.Then the sieving test and laser particle size analyzer test were carried out to measure the particle analysis curve of soil samples.On this basis,the relationship between particle fractal characteristics and hydraulic properties of unsaturated soils is discussed by using fractal theory,and the related theoretical analysis and experimental research have been carried out.The research content and the main results are as follow:(1)The characteristics of phase in unsaturated soil are briefly described,and the significance,test and research methods of the hydraulic characteristics are summarized.At the same time,the advantages and disadvantages of various hydraulic properties research methods are reviewed in a nutshell,and the development history of fractal theory is reviewed for reference.(2)The soil-water characteristic curve is determined by pressure plate apparatus instrument and 7 groups of dry density of three soil samples are selected to test.The more accurate and effective soil-water characteristic curve is obtained,so that it is for practical engineering application analysis.The soil-water characteristic curve of three soil samples is analyzed by using classical model,the advantages and disadvantages of the model and the application range are discussed.Based on the above research,the variation law of fitting parameters of FX model under different dry density is discussed,and the deformation model of FX can be proposed,which has a good effect on describing soil-water characteristic curves under different dry density.Taking Hunan clay as the research object,the hydraulic conductivity of Hunan clay is obtained by variable water head test and instantaneous profile method,and the variation of hydraulic conductivity with dry density is analyzed.(3)In order to obtain the particle-size analysis curve of soil sample in the whole particle size range,the experiment was carried out by means of sieving test and laser particle size analyzer,and the fractal characteristics of particle-size analysis curve were studied based on fractal theory in order to determine the fractal dimension of particle fractal.The foundation is established for the later study of particle fractal characteristics and hydraulic properties.(4)By studying the fractal model of the hydraulic properties and the fractal characteristics of particles,the method of parameter of fractal model of the hydraulic properties is determined and the applicability of fractal model of the hydraulic properties is described.The relationship between the hydraulic properties and the particle analysis curve is established based on the fractal theory,and the experimental data of the Hunan clay is used for verification.It provides a reference for the future research and application of the model,and provides new ideas for the correlational research.