Experimental study on the development of pore pressure in dense sand under the cyclic loading

The past research on sand behavior under cyclic loadings mainly focused on the loose or medium-dense sand. By use of an automatic-controlled triaxial device, experimental study on the Pingtan sand with a relative density of 80% was carried out, under both monotonic and cyclic loadings. Influences of the confining pressure, the lateral stress ratio at consolidation and the cyclic stress ratio on the development of excess pore pressure were analyzed. It is shown that the lateral stress ratio at consolidation and the cyclic stress ratio, which determine the deviatoric stress state of the soil, exert a significant effect on the behavior of dense sand. The excess pore pressure increases relatively fast when the lateral stress ratio at consolidation is high and the deviatoric stress reverses periodically, and the sand exhibits a typical response of cyclic mobility. The excess pore pressure induced by the cyclic loading is relatively low when the consolidation stress ratio is low and the deviatoric stress remains in the domain of triaxial compression. After a certain number of loading cycle, the positive and negative excess pore pressures generated during a loading cycle neutralize each other, and the accumulated excess pore pressure does not increase with the number of loading cycle. The dense sand reaches a cyclic stable state. The phenomenon is not observed in the loose and medium-dense sand according to the literature.