Geotalk

About this event

Category
Educational
Date and time
Jul 1, 2021 16:00 - 17:00

Join the last geotalk of this academic year. There will be an external speaker, see the attached ad:

Centrifuge and DEM investigations into screw piles for offshore applications by Benjamin Cerfontaine

Online Abstract:

Screw piles are composed of one or several helices fixed to a cylindrical or square shaft. They have two main advantages for offshore applications. Firstly, they can be installed in a ‘silent’ manner (by comparison to driven piles), by applying a torque at the pile head, which literally screws the pile into the soil. Secondly, they have a greater tensile capacity than straightshafted piles, thanks to the helix’s embedment, which acts like a plate. One of the key questions for screw pile design is the identification of the crowd force and torque necessary to install them at a desired embedment depth. The crowd force requirement is particularly critical for offshore operations, as the necessary force approaches the upper bound of what could be practically applied by installation vessels. This work investigates how installation parameters can be varied to reduce the installation requirements, and particularly the crowd force. Geotechnical beam-centrifuge experiments were used to create a database of results and validate numerical simulations. The Discrete Element Method was used to investigate micro-mechanical processes underpinning the macroscopic behaviour of screw piles during their installation. The combination of both techniques enabled a meaningful description of installation mechanisms and the development of recommendations beyond current design guidelines. One of the main findings of this study is that screw piles can be safely installed in sand by overflighting, i.e. by applying more helix rotations than recommended for a constant vertical displacement rate. This installation mode was shown to strongly reduce the necessary crowd force and even created some pull-in effect, with the pile actually pulling on the installation rig. This installation was not correlated with degradation of the pile tensile capacity, as could be expected, but by an increase in pile stiffness and capacity.

 

Bio: Dr Benjamin Cerfontaine is lecturer at the University of Southampton (UK). He obtained his PhD at the University of Liège in Belgium, before moving to the University of Dundee (UK) with an MSCA fellowship. He specialised in offshore geotechnical engineering and especially in foundations for offshore renewable energy systems. He worked on innovative anchors, such as suction caissons and screw piles, but also rock anchors for tidal turbines. He combined advanced finite element modelling, Discrete Element Modelling and centrifuge testing to identify key physical mechanisms during installation or loading of offshore foundations.

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