The noncoaxiality of the principal stress direction and plastic principal strain increment has been broadly recognized as an influencing parameter for design of soil structures. Here we performed a series of systematic hollow cylinder experiments to study the effects of stress anisotropy on the noncoaxiality of dense Babolsar and Toyoura sands. A total of 25 undrained torsional shear tests were carried out under constant mean confining pressure, and fixed principal stress directions, α. We investigated the stress-strain behavior of dense sands for different α-directions, and cyclic stress ratio, CSR, under monotonic and cyclic loading conditions. The results show that the noncoaxiality value depends on the CSR, the level of plastic strain, and α-direction. Independent of the principal stress direction, maximum noncoaxiality value was observed at peak shear strength when there is most interlock between sand particles. Minimum noncoaxiality was recorded in α = 45° tests, in which the direction of maximum shear stress coincided with the horizontal bedding plane direction (weakest plane).

主应力方向和塑性主应变增量的非同轴性已被广泛认为是土壤结构设计的影响参数。在这里，我们进行了一系列系统的空心圆柱实验，以研究应力各向异性对致密Babolsar和Toyoura砂的非同轴性的影响。在恒定平均围压和固定主应力方向α的条件下，总共进行了25次不排水的扭剪试验。我们研究了在单调和循环载荷条件下，不同α方向的致密砂土的应力-应变行为以及循环应力比CSR。结果表明，非同轴度值取决于CSR，塑性应变水平和α-方向。与主应力方向无关，当砂粒之间存在最大互锁时，在峰值剪切强度下观察到最大非同轴度值。在α  = 45°测试中记录了最小的非同轴度，其中最大剪切应力的方向与水平垫层平面方向（最弱的平面）一致。