复杂应力条件下长江口原状饱和软黏土门槛循环应力比试验研究

Experimental study of threshold cyclic stress ratio of undisturbed saturated soft clay in the Yangtze estuary under complex stress conditions

针对取自于长江口的海洋原状饱和软黏土,利用土工静力-动力液压三轴-扭转多功能剪切仪,在控制不同初始固结参数的三向非均等固结状态和不排水条件下,分别进行了轴向和扭转双向耦合循环剪切以及循环扭剪等多种复杂循环剪切试验。分别研究了初始大主应力方向角、初始偏应力比、初始中主应力系数以及循环剪切应力模式等因素对门槛循环应力比的影响。试验结果表明,在三向非均等固结条件下,初始大主应力方向角、初始偏应力比对门槛循环应力比影响显著,门槛循环应力比随着初始大主应力方向角与初始偏应力比的增大而明显减小;而初始中主应力系数对门槛循环应力比基本没有影响。循环剪切应力模式对门槛循环应力比具有显著影响,在相同的初始固结应力条件下,循环耦合剪切试验确定的门槛循环应力比明显小于循环扭剪试验所确定的门槛循环应力比。

The soil static and dynamic universal triaxial and torsional shear apparatus facilized in Dalian University of Technology was employed to perform different types of experimental test of undisturbed saturated soft marine clay in the yangtze estuary. The samples were subjected to undrained cyclic vertical and torsional coupling shear and cyclic torsional shear under three-directional anisotropic consolidation conditions with different initial consolidation parameters. The effects of initial orientation angle of maximum principal stress, initial ratio of deviatoric stress, initial coefficient of intermediate principal stress and stress mode of cyclic shear on the threshold cyclic stress ratio were investigated. It is found that the effects of initial orientation angle of maximum principal stress and initial ratio of deviatoric stress on the threshold cyclic stress ratio are remarkable under three-directional anisotropic consolidation; the threshold cyclic stress ratio decreases obviously with increasing initial orientation angle of maximum principal stress and initial ratio of deviatoric stress. However, the initial coefficient of intermediate principal stress has almost no effect on the threshold cyclic stress ratio. It is also shown that the stress mode of cyclic shear has significant effect on the threshold cyclic stress ratio; the values of the threshold cyclic stress ratio determined by the cyclic vertical and torsional coupling shear tests are smaller than those determined by the cyclic torsional shear tests.