Large scale monopiles are one of the preferred foundation types for offshore wind turbines. Pile diameters in current and future projects range between 6 and 11 m while pile penetration depth is typically ranging between 3 to 5 times the diameter. For these dimensions the pile when loaded laterally rotates in a rather rigid manner. This is different to the bending load bearing behavior seen on long and slender piles which were used to establish p-y curves as specified in offshore standards. Within the German research project TANDEM a new design framework is developed based on FE analysis that takes into account the deformation behavior of large-scale monopiles and a high foundation stiffness. The FE models are validated based on large-scale pile load tests conducted in a sand test pit. The FE model uses the CEL method for large deformation. The soil-pile interaction curves are extracted and form the basis to develop and calibrate interaction curves that can be used in a 1D Beam-on-Elastic-Foundation analysis. This paper provides details on the FE modelling and outlines the framework for designing large scale monopiles in sand. Finally, a structure weight comparison is provided that underlines the benefits of the proposed methodology.
Katja Siegl, Jan Dührkop and Severin Spill
Keywords: monopiles, pile-soil-interaction, FEM, CEL, hypoplasticity
Publisher: DFI