Stiffness degradation model of marine soft clay under cyclic loading

A series of cyclic triaxial tests were conducted on Zhoushan undrained marine soft clay with dynamic triaxial instrument to analyze the effects of cyclic loads such as wind and waves on the stiffness degradation characteristics of normally consolidated soft clay. The test results show that the weakening law of soil dynamic modulus closely correlates with CSR. Before the critical cyclic stress ratio CSR is reached, the double-amplitude axial strain $ \varepsilon\mathrm{_{DA}} $ increases linearly with the number of cycles. When the CSR is greater than the critical CSR, the stiffness of the sample degrades significantly with the increase of the number of cycles, so that the soil sample was destroyed. It was found that the influence of different confining pressures on the cyclic weakening of dynamic modulus was effectively captured by CSR. Based on the experimental rules, an empirical formula for soil stiffness variation with the number of cycles, cyclic stress amplitude and confining pressure was established. The stiffness attenuation model of marine soft clay was implemented in the numerical model by using ABAQUS subroutine USDFLD. The research results can provide a reference for the numerical simulation of the bearing performance of offshore wind turbines under long-term cyclic load conditions.