Response of Cyclic-Loaded Bucket Foundations in Saturated Dense Sand

Abstract

One of the major concerns of designing offshore wind turbine foundations is to address the effects of cyclic loading coming from, especially, wave loading. This paper describes the results from a test series on a small-scale mono bucket foundation installed in water-saturated dense sand exposed to cyclic loading with 1.0 Hz. A macro model has been calibrated to fit the test results, and it has been shown that the load frequency has a major influence of the measured rotation of the foundation. Compared to previous tests, the presented test program has been conducted under partly drained conditions due to a higher load frequency, and in addition the foundations have been preloaded by cyclic loads simulating small wave impacts prior to major storm events. The calibrated model shows, in contradiction to previous findings for drained conditions, that two-way loading leads to the largest rotations of the foundation. The reason for this is the partly drained or undrained soil response during testing. The paper also presents a cyclic load response diagram, which is a tool to be used in a predesign of a mono bucket foundation. The diagram gives the designer a quick overview of the cyclic load response and the effect of increasing or decreasing the foundation size.