Control of screw pile installation to optimise performance for offshore energy applications

Screw piles can be used as foundations for offshore energy applications, thanks to their silent mode of installation and considerable uplift capacity, although a significant upscaling of onshore dimensions is necessary. However, the crowd (vertical) force necessary to install upscaled screw piles was previously shown to be far too great for practical installation. Although guidance recommends that the pile's vertical displacement must be one helix pitch (helix height) per each pile revolution, it is shown in this paper that a lower vertical displacement per revolution can significantly reduce the necessary crowd force during installation or even generate some pull-in. In addition, it was shown that the uplift stiffness and capacity of the pile were enhanced by this installation process, at a shallow (relative) depth in sand. This paper gathers 19 centrifuge tests, with varying screw pile geometries (shaft diameter, base shape), sand relative density and advancement rates. A predictive framework for the pull-in potential of a given pile geometry was proposed to assess its ability to be installed with a reduced crowd force.