Research On Fracture Characteristics Of Compacted Clay

Fracture toughness is a parameter that represents the fracture resistance of a material.Compared with the shear strength,there have been fewer researches on the fracture toughness of soil.The shear strength indices of soil are mainly affected by the moisture content and dry density.Researches have also shown that moisture content and dry density of the soil have a significant effect on its fracture toughness.Therefore,this paper aims to study the relationship between the shear strength indices and fracture toughness of soils,which not only enriches the soil strength theory,but also has an important application value for practical engineering.In this paper,the fracture toughness tester developed by ourselves was used to carry out the fracture test of unsaturated clay with different dry density and moisture content.Direct shear test and matrix suction test of unsaturated clay were also carried out.The correlation between fracture toughness,shear index and matrix suction was discussed.Main achievements are presented as follows:(1)When the moisture content is constant,the fracture toughness of unsaturated clay samples increases with the increase of dry density,and a well-fitted linear function relationship is obtained.When the dry density is constant,the fracture toughness first increases and then decreases with the increase of moisture content.The relationship between them is approximately a Gaussian curve.(2)When the dry density is constant,the cohesion of the soil samples gradually decreases with the increase of the moisture content,while the decreasing range decreases.When the moisture content is constant,the cohesion increases with the increasing dry density.(3)When the moisture content is constant,the fracture toughness of unsaturated clay samples increases with the increase of cohesion,and the relationship between fracture toughness and cohesion is a good quadratic function.When the dry density is constant,the fracture toughness of the specimen first increases and then decreases with the increase of cohesion.When fitted to the relationship between fracture toughness and cohesion of unsaturated clay samples,it exhibits a cubic function.(4)The matrix suction of unsaturated clay samples decreases with the increase of moisture content when the dry density is constant.When the moisture content is 20%,the matrix suction values of soil samples with different dry densities are almost equal.When the moisture content is constant,the matrix suction value gradually increases with the increase of the dry density.When the dry density is constant,the fracture toughness of the unsaturated clay samples first increases and then decreases with the increase of the matrix suction of the sample,and there is a good quadratic relationship between them.For the soil samples with a constant moisture content,the fracture toughness value increases with the increase of the matrix suction value,and there is a linear relationship between them.