Bearing performance of offshore bucket foundation with internal cruciform skirt under combined loading

Abstract

Bucket foundation is a promising solution to support offshore wind turbines, due to rapid and quiet installation, low fabrication cost, etc. However, when the foundation is of considerable size (i.e., large diameter with low depth) and is in soft marine sediments, the reliability of the bucket foundation may be low. The large peripheral skirt of a bucket foundation may not confine the internal soil well enough to resist complex environmental loads, leading to a low utilization ratio. This study describes a type of stiffened bucket foundation that employs an internal cruciform skirt, which is an optimization of the conventional bucket foundation. The undrained capacity performance under general loading was systematically investigated by means of a three-dimensional finite element analysis, with the effects of foundation depth and soil strength heterogeneity considered. Parallel comparative analyses for both conventional and solid bucket foundations were also implemented. By comparing both uniaxial and combined loading capacities, the difference in bearing performance was examined and interpreted, and the advantage of employing an internal cruciform skirt and its suitable site conditions was highlighted. Furthermore, a suite of formulae is provided to guide the practical design of the bucket foundation with internal cruciform skirt.