Over the years Tractebel has been involved in several preliminary, basic and detailed designs for scour protections around offshore foundations (C-Power, Northwind, Rentel, Belwind,…). The scour phenomena and the design of a scour protection are very complex and a lot of factors and interfaces have to be taken into account. Lacking clear guidelines and uniform standards regarding the design methodology for a scour protection around offshore wind turbine foundations, Tractebel has developed it’s own “in house” methodology for gravity based foundations, monopiles as well as jacket foundations. This design methodology is based on the requirements of the GL guidelines, completed with the DNV standards for offshore wind and marine operations and specific design guidelines for rock and alternative (e.g. filter bags, mattresses,…) materials, i.e. The Rock Manual (CIRIA/CUR, 2007). The methodology relies on the critical Shields methodology complemented and adjusted with experimental and results of in-field monitoring both on scouring as well as on scour protection behavior. During a MARINET funded research project, under the leadership of Tractebel and in cooperation with HR Wallingford, Ghent University and FEUP, physical model tests on scour protections around monopile foundations were performed at Aalborg University.
Tractebel’s methodology has been successfully applied in several offshore projects and allow appropriate and site specific design assuring the integrity of the stability of the wind turbine foundations under predefined storm conditions. Aside the design itself, a proper, beneficial and economical monitoring and maintenance program makes part of every design.
The Tractebel design methodology for rock works has been recognized by certification authorities and has been successfully applied for the detailed design of the scour protection around gravity based foundations for the C-Power offshore wind farm and for a number of cable protection and cable crossing works for offshore cables in the North Sea. Tractebel’s methodology is state-of-the-art and recognized by developers, certification authorities, scientists and contractors.