Assessment of Monopile-Gravel Wheel Foundations under Lateral-Moment Loading for Offshore Wind Turbines

Abstract

This paper evaluates the lateral performance of a monopile reinforced by a gravel wheel for offshore structures via centrifuge tests and three-dimensional finite-element (FE) modelings. The gravel wheel comprises a ring frame placed on the pile head and filled with large particles to potentially utilize gravel or crushed stone in offshore areas. The results of centrifuge tests and FE analyses demonstrate that the lateral loading capacity of the monopile increases when combined with a gravel wheel, and the improvement depends on the diameter and thickness of the wheel. By means of FE methods, the interaction between the pile and surrounding soils and gravel fill are illustrated to explain how the gravel wheel contributes to the lateral resistance of the hybrid system. Furthermore, an equivalent layer method adopting the conventional p-y curves is suggested to predict the lateral response of the hybrid foundation. This method is validated by comparisons with the centrifuge tests results. Finally, a case study of the monopile-gravel wheel foundation indicates that the gravel wheel is less efficient in configurations where the ultimate capacity of the hybrid system is dictated by the bending capacity of structures rather than the strengths of soils.