Study of dilatancy behaviors of coarse-grained soils in large-scale triaxial test

Using large-scale shearing device, isotropic consolidated-drained triaxial tests under different confining pressures are performed for three relative densities overburden material of Shuangjiangkou earth dam. The dilatancy of coarse-grained materials is investigated; the relationship among dilatancy, relative density and confining pressure are discussed; and applicability of dilatancy equation of modified Cam-clay model and Rowe dilatancy equation for coarse-grained soils are tested. It is found that the confining pressure and initial density influence dilatancy evidently; that is, under low confining pressure coarse-grained soils are characterized by volumetric dilatancy; and with the increasing of confining pressure they exhibit volumetric compression. The increasing of density results in the increase of dilatancy. Phase transformation stress ratio is an important factor affecting dilatancy, which exhibit increasing with the increase of density and linear decrease with the increase of confining pressure. According to the test data, a relationship formula among dilatancy ratio and relative density and confining pressure is obtained. Dilatancy equation of modified Cam-clay model cannot reflect the dilatancy; and Rowe dilatancy equation can reflect the dilatancy of the coarse-grained materials; but when confining pressure is higher it underestimate the compression during compression stage and overestimate the dilatancy during shearing stage.