Deformation characteristics of coarse-grained soil with various gradations

By using large scale triaxial shearing apparatus, consolidated-drained shear tests were conducted on coarse-grained soil with different gradations. In order to describe their deformation rules, three main characteristics of tangent Poisson ratio curves were summarized and the reason was revealed by dividing the movement of soil particles into two kinds: the movement of fine particles and the movement of coarse particles. Then, a volumetric strain expression and a tangent Poisson ratio expression were put forward, and two defects of widely used Duncan-Chang model were fixed. Results calculated from them agree well with test results. There are three parameters, namely L, G and F, in this new model. Parameter L reflects the dilatancy of a specimen and L=4 can be used as a criterion to estimate whether a certain kind of soil has dilatancy quality or not. Parameters G and F relate to the initial slope of tangent Poisson ratio curves, and G=F=0 indicates a special situation which happens in dense granular material of the same diameter. Influences of various gradations on volume deformation are mainly reflected in parameter L which is smaller when there are more gravels in specimens.