Shear strength of expansive soil and its test method

Shear strength parameters are necessary for slope stability analysis of expansive soil. It is difficult to obtain the shear strength parameters of expansive soil because of particularity of expansive soil and complexity of failure mechanism of expansive soil slopes. The researches on the shear strength of expansive soil are availabe, including research system, test methods and valuing principle of shear strength parameters. Focusing on the existence of fissures, it is difficult to measure the shear strength of fissure-plane. At the same time, researchers attempt to reveal the failure mechanism of expansive soil slopes through reduction of shear strength resulted from decrease of water content based on unsaturated soil mechanism. However, the previous records have failed to provide reasonable relationship between slope failure mechanism and shear strength of expansive soil, which leads to failure of numerical analysis in modelling the stability of slope stability in the engineering practice. In the view of shear strength theory, expansive soil is clay and follows the Mohr-Column criterion. Owing to the existence of fissures, expansive soil has the characteristics of both homogeneous and heterogeneous media. So the effect of fissures on the shear strength of expansive soil should be studied in the researches on shear strength behaviour. Based on the in-situ and laboratory tests, it is suggested that the shear strength of expansive soil should be described by the strength of soil block without fissure plane and strength of fissure-plane, and the strength of soil block should be divided into strength with shrinkage crack and without shrinkage crack. Finally, the test method for the shear strength of expansive soil is proposed.