Cyclic softening characteristics of soft clay considering initial shear stress in same or perpendicular direction

Offshore wind turbine foundations are knocked by the integrated action of wind, waves and overturning moment induced by wind turbine operation for long time periods. The soil around the pile is caused to produce cumulative deformation due to the softening induced by the integrated influence of specimen initial and cyclic shear stress, which has an adverse effect on the running performance of the wind turbine. Aiming at this problem, a range of soft clay simple shear tests were conducted. As considering the direction of specimen initial shear stress being the same or perpendicular to the direction of specimen cyclic shear stress, static shear strength and cyclic strength and cyclic deformation and cyclic softening of soft clay were investigated. The results showed that the soil static shear strength decreases with increasing specimen initial shear stress. The direction between specimen initial shear stress and specimen cyclic shear stress has a significant effect on soil cyclic strength. When the direction of specimen initial shear stress is consistent with specimen cyclic shear stress, the softening degree of the specimens is greater. Based on these test results, an improved softening prediction model considering the effect of specimen initial shear stress was proposed.