Effect of effective shearing area on result of direct shear tests

In the existing national standard and specification for geotechnical test in China,the variation of shearing areas of soil body and the interface between soil body and other materials during the shearing process was not taken into account in the interpretation of direct shear test data.For this reason,the relationship between the shear displacement and the effective shearing area of the interface during the shearing process was deduced,and the errors induced by the existing data interpretation method were analyzed.The result shows that the existing method underestimates the shear stress and shear strength parameter of soil body and the interface between soil body and other materials,and that the shearing direction in the direct shear test is preferred to be along the long side of the shear box.