主应力轴循环旋转下高密实粉土稳定性影响研究

为研究主应力轴循环旋转对粉土性状影响，对长江入海口高密实饱和粉土进行了主应力轴180°转幅的循环旋转试验。试验发现，等向固结的高密实粉土在恒定动剪应力比的主应力轴循环旋转下能发生孔压达到初始围压水平的液化破坏，但液化前孔压开展会因动应力水平的不同而呈现以渐变相态点和激变相态点区分的3阶段变化形式，或仅以激变相态点区分的两阶段变化形式。试样应变开展则始终呈现由崩塌点区分的两阶段变化形式，且孔压激变相态点与应变崩塌点同步反映了土体结构崩塌状态，崩塌状态时主应变差双向幅值限制在0.2%～0.4%这一较小范围内。试样进行主应力轴旋转达到崩塌时的应力状态与频率无显著关系，可由 - 空间中一条准不稳定状态线归一化。而以崩塌状态为终点进行归一化的主应力轴循环旋转下孔压振次曲线，可用修正的Seed公式进行较好拟合

Stability of high relative density silt under cyclic principal stress axis rotation

Hollow cylinder samples tests were performed with high-density saturated silt from the sea entrance of the Yangtze River. The stress paths consisted of undrained cyclic principal stress rotation at the range of 180° with different shear stress ratio and frequency. It is found that isotropic consolidated samples would liquefy after cyclic principal stress axis rotation, which is featured by the excess pore water pressure reached initial effective confining pressure. Before the liquefaction, due to the different shear stress levels the development of pore water pressure was divided into three stages by graded phase transformation point and cataclysmic phase transformation point or two stages by cataclysmic phase transformation point. As for the development of strain components, it was divided into two stages by collapse point. Meanwhile the cataclysmic phase transformation point of pore water pressure and the collapse point of strain occurred simultaneously, which reflected the state of structure collapse. Besides the deviator strains when the collapse state occured were limited within a narrow range of 0.2%-0.4%. The stress state of collapse can be normalized in - space with a line when samples underwent cyclic principal stress axis rotation after isotropic consolidation. Furthermore the development of pore water pressure can be fitted well by modified Seed model in which the collapse state was used as the normalized denominator.