Numerical simulation of offshore foundations subjected to repetitive loads

This paper analyzes the long-term offshore foundation that undergoes numerous mechanical cycles. The numerical approach follows the hybrid scheme that incorporates a mechanical constitutive model to extract stress into strains at the first cycle into polynomial-type strain accumulation functions to track the progressive plastic deformation. In particular, the strain function contains the fundamental features that require simulating the long-term response of geomaterials: volumetric strain (terminal void ratio) and shear strain (shakedown or ratcheting), the strain accumulation rate, and stress obliquity. A model is calibrated under zero-lateral strain boundary condition by relaxing model parameters. The semi-empirical numerical scheme is used to simulate two offshore foundations subjected to repetitive loads (i.e., monopile and shallow foundation). Numerical results show that the most pronounced displacements occur during early cycles (N < 100), yet their incremental rate approaches toward an asymptotic value. With stress redistribution around the foundations, vertical and horizontal displacements increase with the number of cycles and the asymptotic displacement increases with higher load amplitude.