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COWI carried out the detailed design of the foundations for Thornthon Bank phase 1.
COWI carried out the detailed design of the foundations for Thornthon Bank phase 1 which comprises 6 turbines, totalling, 30 MW. Fully developed the Thornton Bank Offshore Wind Farm will comprise60 wind turbines. The fist phase comprises 6 wind turbines.
The wind turbines, located some 30 km off the Belgian coast, are planned to be REpower 5 MW turbines, with hub above the sea at 94 m TAW (chart datum corresponding to LAT). The wind turbines are founded at -21.5 m to -27 m TAW and soil conditions are generally sand of medium grain size.
In 2003-2004, COWI carried out a concepts study for alternative foundation solutions, including the innovative conical shell structure, and eventually adopted by the project owner. The prestressed concrete foundation structure is composed of a cylindrical shaft on top of a conical base transferring the loads from the wind turbine directly to the base slab.
The post tensioned structure provides favourable strength and stiffnessproperties as well as fatigue and crack resistance. At the deepest location the foundation extends from -27 m TAW to +17 m TAW. The base diameter is 23.5 m and the shaft diameter is 6.5 m, matchingthe diameter of the turbine tower. The foundation structures are prefabricated on land, and installed at seaby a heavy lift crane, on a pre-installed gravel bed.
The weight of the concrete structure is about 2,700 tonnes. The ballastwill be a combination of sand and heavy fil, suffiient to ensure the stability against overturning moments. The total dry weight may be up to 7,000 tonnes, depending on quantity and type of infil.
Jan RønbergProject Director, Offshore WindTel.: +45 56 40 15 firstname.lastname@example.org
Dredging International n.v., Belgium
Structural design of foundation, Geotechnical design, Hydraulic design of installation stages, Numerical and physical hydraulic modelling of installation stages, including dynamic loads and scour, Appurtenances design, including boat landing and J-tubes, Project follow-up in construction stage.