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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p′-q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。
In order to study the effect of cyclic rotation of main stress axis on silty soil properties, a cyclic rotation test was carried out on the high density saturated silt entering the Yangtze River at a 180 ° rotation of principal stress axis. It is found that the confining high density silt can liquefy under the initial confining pressure when the principal stress axis of the constant dynamic shear stress ratio is cyclically rotated. However, the pre-liquefaction pore pressure will fluctuate due to the dynamic stress level Different from the three phases of the gradual change point of phase transition and the phase transition point, or the two phase change phase of the phase transition point. The specimen strain evolution always shows a two-stage change form which is distinguished by the collapse point. The phase pressure change of the pore pressure reflects the collapse state of the soil structure simultaneously with the collapse point of the strain, and the bidirectional amplitude of the main strain is limited to 0.2% ~ 0.4% within this smaller range. There is no significant relationship between stress state and frequency when the main stress axis rotates to collapse, which can be normalized by a quasi-unstable state line in p’-q space. However, the normalized stress axis of the main stress axis under the collapse state can be used to fit the subsurface pressure curve.