Floating wind turbine anchor piles under lateral multidirectional cyclic loading: experimental investigation 

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The use of open-ended steel piles with catenary mooring lines is a promising solution for anchoring Floating Offshore Wind Turbines (FOWTs) to the seabed. These piles face complex loading conditions, especially in shared anchor configurations, where multiple turbines are anchored to a single pile. This shared anchor approach offers valuable opportunities for optimizing foundations and reducing costs. However, it also increases the severity of cyclic multidirectional loading on the pile, making it essential to accurately predict its response for design optimisation. As part of the GEOLAB project SAM-WT, large-scale experiments were conducted in the geotechnical test pit at the Technical University of Darmstadt. An instrumented model pile with a diameter of 0.325 m and an embedment depth of 2 m was installed in dense compacted sand, representing a real anchor pile at 1/5 scale. A series of lateral cyclic loading packages was applied to the pile, considering first unidirectional cyclic loading to compare with a subsequent multidirectional cyclic loading test. The load was carefully controlled using a pair of actuators connected to the pile via a mechanically articulated system. A range of sensors was installed to measure pile displacement, rotation and applied load at the pile head, as well as strain along the shaft of the pile, while fibre optic sensing was implemented in the surrounding soil to assess the strains around the pile. The analysis presented in this paper focuses on the horizontal displacement of the pile head during cyclic loading, highlighting the differences between unidirectional and multidirectional loading. The findings contribute to a better understanding of pile behaviour under varying loading conditions, supporting the development of more efficient anchor systems for FOWTs.

5th International Symposium on Frontiers in Offshore Geotechnics (ISFOG2025)

13 - Developmental foundation and anchoring concepts: hybrid foundations, ring anchors, helical piles, torpedo, shared anchoring