An Innovative Composite Foundation System for Offshore Wind Turbines: A Finite-Element Approach

Abstract To meet the rising global energy demand, offshore wind turbines (OWTs) are increasingly deployed in deeper marine environments where wind conditions are more favorable. This transition exposes OWTs to intensified environmental loads—such as wind, wave, and rotor-induced dynamic forces—creating unique challenges to foundation designers. To address these challenges and reduce the escalating costs associated with large-diameter monopiles (MP), this study introduces a novel hybrid foundation (HF) system. The HF integrates a shallow circular plate at the seabed with a centrally embedded monopile of reduced diameter and length, offering an alternative to conventional monopile foundations. Through a combined approach of centrifuge modeling and three-dimensional finite-element analysis, this research investigates the influence of HF pile length ( L p ) to plate diameter ( W ) and varying clay soil shear strength ( s u ) and stiffness ( E 50 ) properties on the HF lateral ultimate capacity ( H u ) under eccentric loading conditions. The centrifuge tests simulate overconsolidated clay beds under lateral and overturning loads, and results demonstrate that increasing the L p / W ratio enhances the normalized H u while higher E 50 / s u limits this improvement. Unlike conventional monopiles, the HF system shows reduced sensitivity to MP diameter. Under service load conditions, the HF reduced pile bending moments by 30%–45% and tower tip displacements by up to 200%, confirming its potential to support next-generation OWTs in cohesive soils with improved structural efficiency and cost-effectiveness.