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.

中文翻译：

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多向循环荷载作用下砂体地震压缩试验研究

地震期间地面同时受到水平和垂直运动的影响；然而，现有的大多数地震压缩研究仍然仅限于水平地震运动。因此，在这项工作中，目的是通过实验研究载荷施加的多向性质对沙子地震压缩的影响。对不同相对密度的干砂试样进行了多系列空心圆柱扭剪试验，通过施加垂直和水平循环载荷的各种组合来模拟地震引起的不同应力条件情景。测试结果表明，与水平运动耦合，地震荷载的垂直分量将显着促进砂样中剪切应变和垂直应变的发展。与仅在水平循环应力下的砂样相比，耦合运动下的垂直应变增量可高达 70% 以上。然而，有趣的是，仅叠加垂直运动对垂直应变增长的贡献是有限的。此外，相对密度对垂直应变变化的影响是非线性的，垂直应变的减小率随着相对密度的增加而减小。还有趣地发现，仅叠加垂直运动对垂直应变增长的贡献是有限的。此外，相对密度对垂直应变变化的影响是非线性的，垂直应变的减小率随着相对密度的增加而减小。还有趣地发现，仅叠加垂直运动对垂直应变增长的贡献是有限的。此外，相对密度对垂直应变变化的影响是非线性的，垂直应变的减小率随着相对密度的增加而减小。