P–y curves for bucket foundations in sand using finite element modeling

Pile foundations for offshore wind turbines are often designed using p−y curves, where the soil reaction is given as a function of the pile displacement. The p−y curves are based on experiments done using slender piles, normally used in the oil and gas-industry. The monopiles commonly used today as foundation for offshore wind turbines are much less slender than the piles used to derive the original p−y curves. The bucket foundation is a new and promising foundation concept, which combines the strengths of the monopile with those of the gravity foundation. The bucket foundation is even less slender than a monopile, thus the before mentioned mismatch is even more pronounced. The purpose of this paper is to use 3D finite element modelling in PLAXIS 3D to establish a new p−y curve formulation for the bucket foundation in sand. The new formulation is based on the results of 18 numerical models with varying geometry and soil parameters. In the models, a forced horizontal displacement is applied to the entire bucket foundation and the resulting soil reaction is found by integration of the pressure on the surface of the bucket foundation. The method is applied for increasing displacements to determine several points on the force-displacement curve. In the post-processing of the results, several normalising schemes are applied and a general expression for use on an arbitrary geometry and soil strength is fitted to the results. The expression can be used readily in analytical capacity calculations of the bucket foundation in a sand material.