Investigation of soil reaction curves extracted from 3D FE models-Paper

Paper

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The study investigates why three-dimensional finite element (3D FEM) models predict greater lateral stiffness for offshore wind turbine monopiles than conventional one-dimensional models. Traditional API p-y curves were developed for slender piles, unlike modern monopiles, while the PISA methodology provides updated reaction curves for large-diameter foundations.<br /><br />The authors modelled a monitored monopile in the Belgian North Sea, embedded in medium-dense sand overlying overconsolidated clay. Advanced hypoplastic soil models were calibrated against laboratory and in-situ data. The 3D model was validated against centrifuge tests, showing good agreement with measured pile forces, displacements, bending moments, and soil reactions. The researchers then conducted lateral pushover analyses and extracted p-y curves from the model for comparison with API and PISA curves.<br /><br />The 3D FEM curves were generally stiffer throughout the pile depth and could mobilize greater soil resistance, particularly at peak loading. Their post-peak resistance was similar to PISA predictions. API curves mobilized resistance too quickly at deeper levels, contributing to a lower predicted pile capacity. The findings suggest that existing rule-based curves may underestimate monopile stiffness, potentially helping explain differences between model predictions and monitoring data, including discrepancies in bending moments and natural frequencies.<br /><br />The authors recommend recalibrating PISA curves to better match 3D FEM results and investigating the influence of scour protection on monopile response. Future work will also reassess other PISA reaction components, including base shear and moment and distributed moment.

Keywords

offshore wind turbine

monopile

3D finite element model

lateral stiffness

API p-y curves

PISA methodology

soil reaction curves

centrifuge tests

bending moments

scour protection