主应力轴纯旋转条件下黏土弹塑性变形特性

ELASTO-PLASTIC DEFORMATION BEHAVIOR OF INTACT CLAY SUBJECTED TO PRINCIPAL STRESS ROTATION

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。

A series of undrained pure principal stress rotation and cyclic principal stress rotation tests were carried out on intact clay using a hollow cylinder apparatus. The magnitudes of mean principal stress,shear stress and intermediate principal stress parameter were kept constant during principal stress rotation. The elastic parameters were obtained from the cyclic loading-unloading tests. The elastic and plastic deformation behavior of intact clay induced by pure principal stress rotation was studied. The direction of the plastic strain increment was investigated. Test results show that both the elastic and plastic strain are induced by principal stress rotation alone in undrained condition,the directions of the elastic and plastic strain increment deviated from the principal stress axis. The development of strains is influenced by the intermediate principal stress parameter. The non-coaxial plastic behavior of soil will be overestimated if the influence of elastic strain is not taken into consideration. The plastic strain induced by principal stress rotation depends on both the coaxial and non-coaxial plastic mechanisms.