The Use of Numerical Analysis to Aid the Design of Monopile Foundations for a North Sea Offshore Wind Farm-Paper

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The paper describes how the PISA design approach was applied to monopile foundations for the Triton Knoll offshore wind farm, a 90-turbine project off England’s east coast. Because foundations represented a substantial share of project costs, the study aimed to improve design accuracy and reduce the size and cost of the monopiles.<br /><br />The team combined site-specific CPT profiling and advanced laboratory testing to characterise the Quaternary soils, including stiff glacial tills and dense sands. Soil behaviour was represented using constitutive models calibrated to the test data, capturing small-strain stiffness, nonlinear yielding, and, for dense sands, peak strength and post-peak softening. Single-element finite-element simulations reproduced laboratory stress–strain, pore-pressure, and stiffness responses well.<br /><br />Three-dimensional analyses using Imperial College’s ICFEP code were then conducted for an example monopile approximately 7 m in diameter and embedded 21 m below the scoured seabed. The analyses predicted lateral and moment response under static loading and generated four nonlinear soil-reaction relationships for use in simplified PISA Winkler models: distributed lateral and moment reactions along the shaft, plus base shear and base moment reactions. Results showed strongly nonlinear pile stiffness and distinct soil responses: the clay tills behaved ductilely, while the dense sand developed peak resistance followed by softening. The pile’s centre of rotation remained at roughly two-thirds of its embedded length.<br /><br />The calibrated analyses enabled more representative design and optimisation across the wind farm. The paper reports that improved soil-response modelling supported shallower embedment and lighter foundations than conventional approaches. Related project reporting indicates embedment reductions of about one to two pile diameters and average mass savings exceeding 30% compared with historical monopile trends.

Keywords

PISA design

monopile foundations

offshore wind farm

Triton Knoll

site-specific CPT

Quaternary soils

finite element analysis

soil reaction curves

nonlinear soil behavior

foundation optimization