Suction buckets are expected to be increasingly used as foundations for offshore wind turbine (OWT) projects as they move to deeper water and monopiles become impractically large. Since OWTs are relatively light and operational loads include high overturning moments, potential exists for individual foundations to experience periods of net tension with accompanying (significant) cyclic tension. Foundation design must ensure that these loading conditions do not lead to permanent tilting of an OWT, due to differential foundation movement. This paper presents selected results from a series of centrifuge tests designed to investigate how foundation performance is affected by the signature of the loading, the frequency of the cyclic vertical loading and the average vertical load. Tests were conducted with ‘random’ cyclic vertical loading, applied at different frequencies and with different magnitudes of static and cyclic loading, to replicate the conditions experienced by the windward bucket of a multi-bucket foundation system in sand. The results indicate that under certain drainage conditions, suction buckets can sustain two-way cyclic loading – comprising significant tension load and close to zero average load – with only modest permanent uplift displacement.
Han Eng Low, Fangyuan Zhu, Henning Mohr, Carl Erbrich, Philip Watson, Fraser Bransby, Conleth O'Loughlin, Mark F. Randolph, Mohamed Mekkawy, Thaleia Travasarou and Daniel O'Connell
Keywords: offshore wind turbine, suction bucket, cyclic loading
Publisher: DFI