Physical modelling of cyclically loaded monopiles in sand: the MIDAS centrifuge testing programme

Monopiles are the most common foundation for offshore wind turbines (OWTs), accounting for roughly 80% of installations in Europe. Despite advancements in research, critical knowledge gaps remain, especially regarding the behaviour of monopiles under long-term cyclic loading. Addressing these gaps is vital for enhancing the safety and costeffectiveness of future offshore wind farms and for assessing the life-cycle conditions of existing OWTs. The "MIDAS: Monopile Improved Design through Advanced Cyclic Soil Modelling" project, conducted in the Netherlands by TU Delft, Deltares, NGI, and industry partners, aimed to fill these gaps. Focusing on sandy soils, MIDAS employed a comprehensive methodology combining experimental (element and centrifuge testing), numerical, and theoretical modelling. This paper presents the centrifuge modelling component, detailing the design and implementation of the testing program, including cyclic load definitions, model pile instrumentation, loading configurations, model seabed preparation, and test procedures. Findings indicate that monotonic responses of monopiles with different configurations can be normalized effectively, validating the quality of experimental outcomes in the context of established theoretical models. The study also explores the impacts of stress levels, monopile dimensions, and drainage conditions on cyclic behaviour, contributing valuable insights to the understanding of monopile-soil interactions under cyclic loads.