Study On Permeability Coefficient Of Clay Soil Based On Fractal Theory

Soil permeability is a very important research direction in geotechnical engineering.Relevant scholars have done a lot of theoretical experiments on the permeability of soil,but the permeability mechanism of clay is complex.When calculating the permeability coefficient of clay by the traditional empirical formula,there are some errors between the calculation results and the actual situation,which will have an impact on the reinforcement and repair of actual engineering construction.In this paper,considering the influence of cohesive water on soil permeability,the traditional empirical formula of permeability coefficient is modified based on fractal theory,and the formula for calculating permeability coefficient of cohesive soil is obtained.The formula is further validated by indoor seepage test.The main work and achievements of this paper are as follows:(1)When the traditional empirical formula of permeability coefficient is used to calculate the permeability of clay,the calculated results are often larger than the actual permeability coefficient of soil samples.Therefore,it is necessary to revise the traditional empirical formula of permeability coefficient before it can be applied to study the permeability characteristics of clayey soil.In this paper,Carson-Carmen permeability coefficient formula is selected as the traditional empirical formula of permeability coefficient,which is modified by the concept of effective void ratio.Based on fractal theory,the effective void ratio function in the revised formula is deduced,and the empirical formula of Carson-Carmen permeability coefficient is modified to the formula of permeability coefficient applicable to cohesive soil.(2)In order to verify the accuracy of the revised formula for calculating permeability coefficient,two kinds of cohesive soils are selected for permeability test Before the permeability test,the basic physical parameters of cohesive soils used in the test are determined,including particle size distribution,specific gravity,maximum dry density and minimum dry density.When conducting indoor permeability test,because the permeability of cohesive soil is poor,variable head permeability test is used to measure the permeability coefficient of cohesive soil,and the test data are collated and analyzed.(3)Based on the fractal theory,the functional relationship between the fractal dimension of clayey soil and the slope of particle gradation curve is deduced,and the fractal dimension of soil sample used in the experiment is obtained.The traditional empirical formula of permeability coefficient and the revised formula of permeability coefficient based on fractal theory are used to calculate the permeability coefficient of clay used in the test,and the comparison and analysis with the measured data are made to verify the accuracy and rationality of the revised formula of permeability coefficient in this paper.Based on the study of soil permeability by scholars at home and abroad,the traditional permeability coefficient formula is revised based on fractal theory,and the permeability tests of clay samples with different dry densities are carried out.The calculation results of the traditional permeability coefficient formula and the modified permeability coefficient formula are compared with those of the permeability test results,and it is found that the calculated results of the modified formula are worse than those of the test results.The correctness of the revised formula is verified.This study combines the fractal theory of porous media with the permeability study of clay,reveals the mechanism and essence of the permeability of clay,and provides an important theoretical guidance for seepage control and foundation settlement of civil engineering in the future.