Study On Tensile Strength Of Compacted Clay

The tensile strength of soil is often ignored in geotechnical engineering because it is small and difficult to measure. In recent years, however, more and more engineering problems related to the tensile strength of soil are encountered, such as soil fracturing and collapsing, hydraulic fracture of core wall in earth-rock dam. Therefore, it is urgent to conduct research on the tensile strength of soil. The study on the tensile behaviors of soil not only contributes to the theory of soil strength, but also is important to solve the practical engineering problems.There is not standardized apparatus and experimental method for tensile strength of soil yet. In this thesis, the self-developed strain-controlled uniaxial tension apparatus is used to conduct tensile tests on compacted soils with various moisture content and dry density. Compared with the tensile strength, more research has been carried on the shear strength, and the strength of unsaturated soil is largely dependent on the matric suction of the soil. Therefore, the shear strength and the matric suction of the unsaturated clay are also included in this thesis.Main achievements are presented as follows:(1) The stress increases with the increasing strain, and the stress-strain curve rises before the tensile stress reaches the tensile strength of the specimen. When the dry density is constant, the slope of the stress-strain curve increases as the moisture content decreases, and vice verse. After the tensile stress reaches the tensile strength of the specimen, the stress decreases with the increasing strain and the stress-strain curve declines. The tensile stress reduces sharply and the stress-strain curve declines rapidly when both the moisture content and the dry density are small. The tensile stress reduces slowly and the stress-strain curve declines when both the moisture content and the dry density are great.(2) When the dry density is constant, the tensile strength of the unsaturated clay decreases with the increasing moisture content. When the moisture content is constant, the tensile strength of the unsaturated clay increases with the increasing dry density. A well-fitted binary function relationship is derived.(3) When the dry density is constant, the cohesion of the unsaturated clay which changes with the increasing moisture content is not a monotonous process:the cohesion decreases at first then increases when the dry density is small, the cohesion decreases when the dry density is great. The internal friction angle decreases on a whole when the moisture content increases.(4) The cohesion of the unsaturated clay increases as the dry density increases when the moisture content is constant. And there is no obvious correlation between the internal friction angle and the dry density.(5) The tensile strength increases as cohesion increases overall. We can get a well-fitted quadratic function between the cohesion and the tensile strength. There is no obvious correlation between the internal friction angle and the tensile strength, and we cannot get a conventional regression function between them.(6) The matric suction of the unsaturated clay decreases as the moisture content increases when the dry density is constant. The matric suction of the unsaturated clay represents varying-degree increments as the dry density increases when the moisture content is constant. The tensile strength of unsaturated clay increases as the matric suction increases when the dry density is constant. A good logarithmic relationship between them has been obtained. The tensile strength of unsaturated clay increases as the matric suction increases when the moisture content is constant. There is a good quadratic function between them.