A novel offshore foundation concept, the Keystone “twisted jacket”, was deployed in 30 m water depth at a site off the Hornsea, UK coast in 2011. Structural monitoring instrumentation was installed on the foundation at the fabrication yard. This paper describes the monitoring of the structure in the first 15 months since installation, and the analyses of foundation behaviour revealed by the data gathered. This foundation concept consists of a relatively light-weight "twisted jacket" structure that includes: (i) a central pile driven vertically into the seabed; (ii) a guide structure that is lowered over the central pile, and; (iii) raking piles that are installed through the guide structure prior to grouting the piles into the guide sleeves. Considering the sensitivity of wind turbines to dynamic stiffness and resonance effects, an accelerometerbased monitoring strategy was implemented on the substructure. The derived structural frequencies were compared to the original design conditions, where the structure was observed to behave in a manner which was stiffer than anticipated. The resulting accelerations were also compared to the metocean data measured at the site, which allowed inferences to be made about the dynamic movements of the structure.
P. Doherty and B. Casey
Keywords: None provided
Publisher: DFI