中文摘要：

采用空心圆柱扭剪仪对原状软黏土进行了不排水条件下的主应力轴纯旋转试验，即主应力轴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。重点研究了中主应力系数对原状软黏土在主应力轴纯旋转条件下的孔压和变形特性的影响，基于试验结果对主应力轴纯旋转的影响机理进行了分析。试验结果表明：即使3个主应力的值都保持不变，原状黏土的孔压和应变也会随着主应力方向的旋转而累积，经历主应力轴的旋转后土体刚度减小；主应力轴连续旋转时主应变增量方向与主应力方向存在显著的非共轴现象：中主应力系数对主应力轴旋转条件下孔压和应变的开展以及刚度衰减有显著的影响，而对非共轴特性的影响较小。电镜扫描结果表明经历主应力轴旋转后黏土颗粒破碎聚集成较大的团粒，大孔隙显著减少，颗粒和孔隙分布趋于均匀，主应力轴旋转的影响机理可以归结为主应力轴旋转对土体微观结构的扰动和破坏。

英文摘要：

In this study, a series of undrained pure principal stress rotation tests on intact clay are carried out by use of a hollow cylinder apparatus. The magnitudes of the mean principal stress, shear stress and intermediate principal stress coefficient are kept constant during the principal stress rotation. The influence of the intermediate principal stress on pore water pressure and deformation behavior is studied in particular. The mechanism of the effect of the principal stress rotation is analyzed. The test results show that the pore pressure and strain of intact clay accumulate with the principal stress rotation even when the three principal stresses are kept constant. The directions of the principal strain increment and the principal stress are not coaxial. The influence of the intermediate principal stress coefficient on pore pressure and strain accumulation as well as stiffness degradation is significant, but not obvious on the non-coaxial behavior. The mechanism of the effect of the principal stress rotation can be attributed to the disturbance of the microstructure of intact clay.