Centrifuge modelling of intermediate piles subjected to multidirectional cyclic lateral loading

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The expansion of offshore wind energy highlights the potential of Floating Offshore Wind Turbines (FOWTs) for deeper waters, where fixed-bottom turbines face technical and economic challenges. Shared mooring systems present a promising solution for the mass deployment of FOWTs, potentially reducing mooring costs and carbon footprint. However, shared anchoring poses increased risks of cascading failures, necessitating rigorous design considerations for complex loading scenarios, including strong multi-directional cyclic loads. This study, conducted within the MUTANC project, investigates the response of shared anchor foundations under multidirectional cyclic loading using physical modelling at the geotechnical centrifuge facility of Gustave Eiffel University. The experimental setup mimicked anchor piles shared by multiple floaters, subjecting them to complex multi-directional cyclic loading paths. One test, specifically a 'cross' test with perpendicular cyclic loads relative to a constant principal axis load, was meticulously analysed. Results reveal significant ratcheting effects under high-amplitude multidirectional two-way cyclic loading, particularly in the principal direction, where no deformation is expected from an equivalent test without the maintained load. Comparative analysis with unidirectional cyclic tests indicates that multidirectional loading increases accumulated displacements for high-amplitude cycles, underscoring the need to account for load directionality in design to minimise conservatism. These findings provide preliminary insights into the performance and design optimisation of shared anchors for floating wind applications and offer guidelines for designing monopiles to withstand multi-directional cyclic loads for bottom-fixed offshore wind applications.

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

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