中文摘要：

很多情况下圣维南假设（主应变增量方向和主应力方向相同）对土体材料并不成立，即土体材料的主应变增量方向和当前主应力方向存在非共轴特性，土体这一特性已经被很多试验所证实。利用浙江大学5Hz空心圆柱扭剪仪对杭州原状软黏土进行了主应力轴连续旋转、往复循环旋转以及主应力方向角和剪应力同时增大等3种应力路径下的试验，对原状软黏土的非共轴性及其影响因素进行研究。不同主应力轴旋转条件下原状黏土的主应变增量方向和主应力方向之间都存在明显的非共轴现象，与砂土类似但表现形式并不完全相同。初始剪应力较大或主应力轴旋转的同时增加剪应力非共轴性都会减弱；主应力轴往复旋转时，中主应力系数b≠0会使非共轴性更为复杂：经历主应力轴逆向旋转之后非共轴角会增大。此外，试验结果还表明随着扭剪应变的显著增大，非共轴角会减小，甚至出现负值。

英文摘要：

The Saint Venant＇s postulate is inapplicable to soil materials, namely there is a deviation between the major principal stress and strain increment directions. A series of tests with principal stress rotation are carried out on intact Hangzhou soft clay with ZJU-HCA. The stress paths under continuous rotation, cyclic rotation of principal stress and increasing principal stress direction angle and deviatoric stress are designed to study the non-coaxiality behaviors and influence factors. The non-coaxiality between the principal stress and strain increment directions is remarkable and quite different from that of sands. The degree of non-coaxiality in the tests with larger deviatoric stress or principal stress rotation with increasing deviatoric stress is smaller. In the cyclic principal stress rotation tests, the non-coaxiality is more complex when b≠0. The non-coaxiality is more significant when the samples experience reverse rotation of the principal stress. Additionally, the degree of non-coaxiality decreases as the development of shear strain and sometimes even negative values is investigated in non-coaxial angle.