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利用空心圆柱扭剪仪对原状黏土开展系列主应力轴单纯连续旋转和循环旋转条件下的不排水试验,主应力轴单纯旋转过程中平均主应力、剪应力和中主应力系数都保持不变。通过循环加载卸载试验得到黏土不排水条件下的弹性参数。对主应力轴连续旋转引起的黏土弹性变形和塑性变形特性进行研究,分析主应力轴旋转引起的塑性应变增量方向的变化。试验结果表明,不排水条件下主应力轴单纯旋转会引起黏土的弹性和塑性变形,弹性应变增量和塑性应变增量的方向都与相应的应力方向不共轴。中主应力系数对变形的开展有较大的影响。虽然弹性应变分量较小但对应变增量方向的影响仍较大,在主应力轴纯旋转应力路径下,不考虑其影响可能会高估土体的塑性非共轴特性。主应力轴旋转引起的塑性应变的开展受共轴和非共轴塑性变形机制共同控制。
Unconsolidated tests were carried out on the intact clays using a simple cylindrical torsional shear tester under simple continuous rotation and cyclic rotation. The average principal stress, the shear stress and the mid-principal stress coefficient remained unchanged during the simple rotation of the principal stress axis. Through cyclic loading and unloading tests, the elastic parameters of undrained clay were obtained. The elastic deformation and plastic deformation characteristics of clay caused by continuous rotation of principal stress axis are studied, and the change of plastic strain increment direction caused by rotation of principal stress axis is analyzed. The experimental results show that simply rotating the principal stress axis under undrained conditions will cause the elastic and plastic deformation of clay. The elastic strain increment and the plastic strain increment direction are not coaxial with the corresponding stress directions. The main stress coefficient has a greater impact on the deformation. Although the elastic strain component is small but the influence on the direction of strain increment is still large, it is possible to overestimate the plastic non-coaxiality of soil under the purely rotational stress path of the principal stress axis without considering its influence. The development of plastic strain caused by the rotation of the principal stress axis is jointly controlled by the coaxial and non-coaxial plastic deformation mechanisms.