Strain accumulation of marine clay under long-term cyclic loading: experimental study and modeling

Abstract

Offshore structures are frequently subjected to hundreds of thousands of cyclic loadings over their service life due to environmental factors such as wind and waves. Despite extensive research, accurately predicting the permanent deformation of marine soils under long-term cyclic loading remains a challenging issue. In this study, a series of undrained cyclic triaxial tests (CTTs) were conducted on marine clays, considering variations in cyclic deviatoric stress, initial static shear stress, and initial mean effective stress. The experimental results indicate that the permanent axial strain increases with cyclic stress ratio (CSR), initial static shear stress, and initial mean effective stress. Furthermore, the shear strain amplitude is found to be positively correlated with the rate of permanent strain accumulation. Based on these findings, an empirical model is proposed to estimate the permanent strain of clay, incorporating the effects of shear strain amplitude and other key influencing factors. The model is further refined through the incorporation of a reference shear strain parameter, which accounts for the influence of plasticity index. Finally, the modified model was validated using datasets from previous studies. A comparison between the predicted and measured results demonstrates the model's effectiveness in capturing the permanent strain behavior of clays subjected to cyclic loading.