• Investigation of storm-reconsolidation episodes on a monopile in a natural clay. • An advanced constitutive model is used to predict the cyclic response of clay. • Centrifuge test results are accurately reproduced. • Overconsolidation ratio and clay structure influence the tendency for soil hardening following each storm-reconsolidation episode. • A reduction in the monopile’s cumulative peak lateral displacement is observed after each storm-reconsolidation episode. Monopiles for supporting offshore wind turbines (OWTs) in clay deposits are subjected to intermittent cyclic remoulding during severe and extreme weather events, followed by reconsolidation during normal operating conditions. This study uses three-dimensional (3D) finite element analysis with a kinematic hardening soil constitutive model to assess the resulting response. The constitutive model was calibrated using monotonic and cyclic triaxial experiments, and the monopile-clay interaction was validated against a centrifuge model test in Malaysian kaolin, with results presented in terms of load-displacement relationship. A 15MW OWT supported on a 10 m diameter monopile in a soft natural clay typical of most offshore sites was analysed under operating and non-operating conditions, incorporating combined wind and wave loading with intervening reconsolidation periods. The effects of overconsolidation ratio (OCR), clay structure, and average shear stress were investigated through pore water pressure accumulation, shear strain evolution, and effective stress recovery, and these mechanisms were linked to the global pile response. Excess pore water pressure was generated during extreme loading, reducing the effective stress around the monopile, with partial recovery observed during reconsolidation. OCR and clay structure were shown to govern the monopile’s response, with reduced tendency for soil hardening at higher OCRs. In general, the cumulative peak lateral pile displacement at the mudline decreased after each storm reconsolidation episode. Often overlooked in design practice, this beneficial effect can be predicted using the approach herein. The results form the basis for validating digital twin models for long-term monitoring and asset management of monopile-OWT service life.
Aghedo et al. (Thu,) studied this question.