Undrained Long-Term Cyclic Degradation Characteristics of Offshore Soft Clay

Abstract

To design for offshore pile foundations, it is necessary to account for the degradation of stiffness and strength of saturated soft clay under long-term cyclic loading. Hence using the laboratory GDS test apparatus, a series of static and cyclic undrained triaxial tests were conducted on isotropically and anisotropically consolidated natural undisturbed saturated 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 reduce with the increase of the cyclic stress ratio and the progressive number of cycles. On the other hand, anisotropic consolidation and lower effective consolidation pressure decelerate the degradation of stiffness under the same cyclic stress ratio. The dynamic deviatoric stress level was 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.