Many geotechnical problems, such as buried pipeline–soil interaction and wave loading on sand seabeds, require the soil behaviour at relatively low effective stresses as compared to that in typical geotechnical practice. Monotonic and cyclic direct simple shear (DSS) tests were conducted on dry sand under constant normal stress, ranging from 12.5 kPa to 400 kPa, to investigate the effects of confining pressure on stress–strain behaviour. The tests were conducted using a combined advanced dynamic cyclic simple shear apparatus, which has a high-precision feedback system for controlling and measuring the forces and displacements while maintaining a high level of accuracy, which is essential, especially for tests at low normal stresses. The monotonic test results with this advanced system show an increased shear to normal stress ratio, thereby the mobilized friction angle, at the low-stress level compared to that of high normal stresses, as observed in some previous studies. The cyclic test results show that the load–displacement behaviour and cyclic compaction are governed by the normal stress. The sand becomes densified when the applied shear strain amplitude is greater than its threshold value. In constant strain amplitude cyclic loading, the lower normal stresses result in higher compaction; however, an opposite trend exists in constant stress amplitude cyclic tests.

与典型的岩土工程实践相比，许多岩土工程问题，例如埋地管道-土壤相互作用和沙质海床上的波浪载荷，需要在相对较低的有效应力下的土壤行为。在 12.5 kPa 至 400 kPa 的恒定正应力下对干砂进行单调和循环直接简单剪切 (DSS) 测试，以研究围压对应力应变行为的影响。测试是使用组合的先进动态循环简单剪切装置进行的，该装置具有用于控制和测量力和位移的高精度反馈系统，同时保持高精度，这是必不可少的，尤其是在低法向应力下的测试中。这种先进系统的单调测试结果显示剪切与法向应力比增加，因此，与之前的一些研究中观察到的一样，与高法向应力相比，低应力水平下的动摩擦角。循环试验结果表明荷载-位移行为和循环压实受正应力控制。当施加的剪切应变幅度大于其阈值时，沙子变得致密。在恒定应变振幅循环加载中，较低的法向应力导致较高的压实；然而，在恒定应力幅度循环测试中存在相反的趋势。当施加的剪切应变幅度大于其阈值时，沙子变得致密。在恒定应变振幅循环加载中，较低的法向应力导致较高的压实；然而，在恒定应力幅度循环测试中存在相反的趋势。当施加的剪切应变幅度大于其阈值时，沙子变得致密。在恒定应变振幅循环加载中，较低的法向应力导致较高的压实；然而，在恒定应力幅度循环测试中存在相反的趋势。