Centrifuge tests on effects of episodic cycling and reconsolidation on large-diameter monopile foundations for offshore wind turbines

Typhoons frequently occur along the southeastern coast of China, and offshore wind turbines often suffer from multiple cycling and reconsolidation during their service life. However, there is currently limited research on effects of cycling and reconsolidation. To address this, a series of centrifuge tests was conducted on two types of large-diameter monopile foundations in soft clay with different amplitudes, aiming to reveal and quantify the impact of episodic cycling and reconsolidation effect on key design indicators such as cumulative displacement and pile head stiffness of large-diameter monopiles. The test results show that under the same cyclic load amplitude, after two episodes of cycling and reconsolidation, the maximum stiffness of the pile head of monopile foundation can increase by 1.5 times compared to the initial stiffness. This significantly reduces the cumulative displacement of the monopile, with a maximum reduction of 63%. Therefore, if the episodic cycling and reconsolidation effect on the subsequent cyclic response of a monopile is not considered in the design process, and the cumulative displacement of a monopile under each extreme typhoon is directly accumulated, it will seriously overestimate the cumulative displacement of the pile, leading to a conservative design.