Cyclic Loading of Helical Pile as Anchor for Floating Windturbines: Centrifuge Tests-Paper

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The study evaluates single-helix piles as potential anchors for floating offshore wind turbines, focusing on installation and performance under cyclic tension. Researchers conducted 1:10-scale centrifuge tests at 10g using a rigid steel model pile installed in saturated, dense Hostun sand. The pile was installed in flight to an embedment of 7.4 helix diameters, then subjected to monotonic tension and force-controlled cyclic loading.<br /><br />Installation at 1 and 13 rpm produced a 15% difference in measured installation torque. However, the maximum tensile resistance differed by less than 4%, indicating little effect of rotation rate on ultimate tension capacity in these tests.<br /><br />Eighteen cyclic tests examined how load levels affect displacement accumulation. Tests were classified by whether the anchor-head displacement stabilized, accumulated moderately, or reached a limit of 10% of the helix diameter within 1000 cycles. Ten tests were stable, five were metastable, and three were unstable. The results suggest a safety factor of 1.6 may provide a stable response for the studied pile, though the limited test set does not establish precise boundaries between the response zones.<br /><br />Overall, the centrifuge experiments indicate that the tested helical pile can resist cyclic tensile loading, and that installation speed has little influence on its monotonic tension capacity. Further testing, including pore-pressure measurements and a wider range of loading conditions, is needed to refine design guidance.

Keywords

single-helix piles

floating offshore wind turbines

centrifuge tests

cyclic tension

installation torque

tensile resistance

Hostun sand

embedment depth

safety factor

helical pile anchors