Mechanisms of shear strain accumulation in laboratory experiments on sands exhibiting cyclic mobility behavior

Abstract

The factors and mechanisms controlling the accumulation of shear strains of clean uniform sands exhibiting cyclic mobility behavior under level-ground conditions are examined. This phenomenon is investigated through a series of constant-volume cyclic direct simple shear (DSS) tests subjected to uniform and irregular loading conditions, and undrained cyclic element tests collected from the literature. Experimental data show that the rate of shear strain accumulation per loading cycle depends on the relative density, cyclic stress amplitude, and effective overburden stress. Mechanisms of shear strain accumulation are investigated by decoupling the shear strain developed in each loading cycle in two components: γ0, developed at near-zero effective stress, and γd, developed during dilation. Results show that γ0 mostly depends on the shear strain history, while γd depends on the cyclic stress amplitude and relative density. These dependencies of γd and γ0 are used to provide an explanation for the gradual decrease of the rate of shear strain accumulation that is observed while increasing the number of post-triggering loading cycles in tests performed on dense specimens.