Experimental Investigation on Seismic Compression of Sand Subjected to Multidirectional Cyclic Loads

The ground is simultaneously subjected to both horizontal and vertical motions during earthquakes; however, the majority of existing studies on seismic compression are still limited to the horizontal earthquake motions only. In this work, the objective is therefore to experimentally investigate the effects of multidirectional nature of load application on seismic compression of sand. Multiple series of hollow cylindrical torsional shear tests were conducted on dry sand specimens with different relative densities, where different scenarios of stress conditions induced by earthquakes were simulated by applying various combinations of vertical and horizontal cyclic loads. Test results revealed that coupling with horizontal motions, the vertical component of seismic loads would significantly contribute to the development of both shear and vertical strains in the sand specimen. The increment in vertical strain under coupled motions could be up to over 70% compared to its counterpart for the sand specimen under horizontal cyclic stress alone. Nevertheless, it is also interestingly found that the contribution of superimposed vertical motion alone to the growth of vertical strain is limited. Besides, the effect of relative density on the change of vertical strain is nonlinear, and the decreasing rate of vertical strain diminishes with the increase of relative density.