Current international guidance recommends that cyclic loading effects are considered in pile design. However, methods for quantifying these effects on axial capacity are not well developed. Simplified methods exist, including generalised interaction diagrams, but they may not be able to address site-specific aspects of soil behaviour, layering, pile geometries or cyclic loads. Applying 'one size fits all' cyclic loading factors is likely to be either inappropriate or uneconomic in wind farm applications, where turbines may be spaced kilometres apart with geology and water depth varying between positions. This paper describes how carefully controlled laboratory tests on site-specific soils allowed case-by-case cyclic analyses to be developed for a major wind farm site in the North Sea. Interpretation of cyclic laboratory tests on sand and clay, within an effective stress framework, allowed the potential cyclic degradation of pile shaft friction to be assessed. The practical approach outlined is shown to provide a feasible route to assessing turbine-specific cyclic factors for offshore pile design.
Proceedings of the 8th International Conference, 12-14 September 2017, Royal Geographical Society, London, UK