Installation and axial capacity of the Sheringham Shoal offshore wind farm monopiles – a case history

Abstract

The Sheringham Shoal offshore wind farm is located in the North Sea, approximately 20 km north of the Norfolk coast. At this location, Quaternary sediments of the Swarte Bank, Egmond Ground, Bolders Bank and Botney Cut Formations are found directly on top of the Cretaceous chalk. The chalk is thought to be similar to the high porosity upper Campanian (84-74 million years) chalks found in Norfolk and to be comprised of the Paramoudra and Beeston Chalks. Monopile foundations we re installed at the Sheringham Shoal Offshore Wind Farm in Summer 2011. Low driving resistances were encountered during installation of some of the monopiles, particularly in areas with shallow subcropping chalk. In some instances pile ‘run-out’ occurred (i.e. continued penetration under the weight of the pile and hammer alone). This paper presents a case history of the available information, including an overview of the geological and geotechnical conditions at the site together with the pile driving records. Results from back-analysis of the driving records to assess the Soil Resistance to Driving (SRD) are presented and provide possible explanations for the observed pile driving responses. The long-term axial capacity of the monopiles is discussed. The properties of the chalk are based on a review of the available literature and site-specific laboratory and field tests.