Bearing Behavior of a Monopod Bucket Foundation Supporting an Offshore Wind Turbine in Sandy Soils

A monopod bucket foundation supporting an offshore wind turbine structure is subjected to lateral loading on account of combined wind and wave action, in addition to vertical loading from the self-weight of the turbine structure. In this numerical study, the bearing behavior of the bucket foundation in medium dense and very dense sands is investigated for varying bucket geometries, superstructure loads, and lateral loading cases. The nonlinear stress-strain response of the sandy soil is incorporated. The results of the modeling are described and evaluated in terms of the variations of displacement and rotation responses, ultimate and allowable lateral load capacities, depths of rotation center, surrounding soil deformation, and failure mechanisms. Interaction diagrams between lateral load capacity and resisting moment capacity for various limit states are presented, and their differences are brought out. As the design is dominated by requirements resulting from serviceability limit state, predictive expressions are proposed for the depth of rotation center, initial stiffness, and allowable lateral load capacity to serve as preliminary design guidelines for a monopod bucket foundation in sandy soils. The expressions are suitable for interpolation within the range of realistic parameters considered in the study.