Abstract
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.
Highlights
Screw piles are composed of one or several steel helices connected to a central shaft or core (Perko, 2009; Lutenegger, 2011)
Both figures show that a significant compressive force is necessary to achieve the advancement ratio (AR) recommended by the standards (AR =1±0.15, according to BS 8004 (2015)), i.e. to achieve a pitch-matched installation
This paper investigates the effect of installation parameters on the installation requirements as well as the uplift capacity of screw piles
Summary
Screw (or helical) piles are composed of one or several steel helices connected to a central shaft or core (Perko, 2009; Lutenegger, 2011). Screw piles of relatively small dimensions (helix diameter ranging from 150-600 mm; Perko, 2009) are typically used onshore (Tang and Phoon, 2020), e.g. to anchor light structures such as telecommunication towers (Schiavon et al, 2016a), foundations for buildings (Komatsu, 2007), bridges (Harnish and El Naggar, 2015) or modern offshore energy applications (Byrne and Houlsby, 2015; Spagnoli et al, 2020) for which they have three main advantages Their embedded helical plate provides significant uplift resistance (Giampa et al, 2017; Hao et al, 2019; Cerfontaine et al, 2020b). They could be removed by reverse rotation (Ding et al, 2019) to allow complete decommissioning
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