Concept Design Study of Laterally Loaded Monopiles in Sand-Paper

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The study evaluates the PISA numerical-based design method for laterally loaded offshore wind monopiles in dense North Sea sand, comparing it with conventional p-y design. PISA uses a one-dimensional Timoshenko beam model with four nonlinear soil-reaction components, calibrated against three-dimensional finite-element analyses. The soil response was modelled using the HSsmall constitutive model and realistic depth-varying soil properties.<br /><br />For a concept design with an 8 m diameter pile, an 80 mm wall thickness and a 35 m load lever arm, the serviceability limit state (SLS) governed the required penetration depth. PISA indicated a minimum depth of approximately 24 m, compared with about 25 m using the p-y method. The calibrated PISA model closely reproduced the 3D model response, with approximately 95% accuracy for the assessed load–displacement curve.<br /><br />For the ultimate limit state (ULS), PISA suggested a shorter pile than the p-y approach: the p-y method required roughly 17–18% greater penetration to achieve comparable capacity. Thus, p-y may provide similar design depths when SLS governs, but can predict lower capacity and longer piles when ULS is decisive or greater permanent rotation is allowed.<br /><br />The findings are indicative rather than definitive. The analyses considered static monotonic loading and excluded cyclic effects, installation, scour and loading-rate effects; the numerical soil model also lacked advanced laboratory-test calibration. Further validation against centrifuge or full-scale tests is needed.

Keywords

PISA design method

offshore wind monopiles

laterally loaded piles

dense North Sea sand

p-y method

Timoshenko beam model

soil reaction components

HSsmall constitutive model

serviceability limit state

ultimate limit state