Degradation of stiffness and strength of offshore saturated soft clay under long-term cyclic loading

To design offshore pile foundations, it is necessary to consider the degradation of stiffness and strength of saturated soft clay under long-term cyclic loading. Using the cyclic triaxial test apparatus with bender element system, a series of static and cyclic undrained triaxial tests are conducted on isotropically and anisotropically consolidated natural undisturbed soft clay with the shear wave measured by bender element system during cyclic loading. The experimental results show that under the same consolidated condition, the undrained strength and stiffness of soft clay markedly decrease with the increase of the cyclic stress ratio and the progressive number of cycles. On the other hand, the anisotropic consolidation and lower effective consolidation pressure decelerate the degradation of stiffness under the same cyclic stress ratio. It is unable to show the reduction of stiffness and strength of offshore saturated soft clay correctly under cyclic loading for different consolidation modes by the relative deviatoric stress level. The dynamic deviatoric stress level is introduced considering the effects of effective confining pressure, consolidated static deviatoric stress and dynamic deviatoric stress. The dynamic deviatoric stress level is further used to describe the reduction of stiffness and strength of saturated soft clay under cyclic loading.