Owing to the high demand for energy supply, the use of offshore wind turbines as a renewable and environment-friendly energy source has been remarkably increased. After installation in the ocean, the offshore structure foundations and soil that support them are subjected to cyclic loading from wind and waves. In this study, laboratory experiments were conducted to evaluate the shear behavior characteristics of the marine soil subjected to cyclic loading. Utilizing a cyclic direct simple shear (CDSS) test apparatus, the undrained shear failure behavior of marine silty sand was investigated. The results show that the cyclic behavior and permanent shear strain were different depending on the average shear stress ratio. Failure criteria were proposed by analyzing the failure behaviors corresponding to various cyclic loadings. The proposed failure criteria may be used for the preliminary design of offshore structure foundations.

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