Technology from Europe:
The Netherlands

Pilings for world’s largest windmill park

Hydrohammer used to install 80 foundation piles for windmill park off Denmark.

By order of Elsam, the largest energy supplier in Denmark, MT-Hojgaard, a Danish contractor, placed the foundation piles for the Hornsrev offshore windmill park last summer. For this unique pile work, they opted for an IHC Hydrohammer (IHC) type S-600, together with an IHC pile handling tool. Europe kept a close watch on the construction of the largest windmill park in open sea. In four months time, 80 steel piles, with up to 4-m diameters and lengths of 30 m, were driven 25 m into the seabed. 

The park, located 17 km off the coast of Jutland, Denmark, comprises 80, 2-mW wind turbines placed in eight rows of 10 each over a distance of 560 m. The installation equipment had to meet specific requirements of offshore conditions and limited water depth of 7 to 13.7 m. For handling and driving the enormous, 130-mt piles with the S-600, they opted for a jackup, which gave a stable work platform on which heavy seas did not impact working conditions. 

The project chose the single-pile concept, i.e., driving one pile per windmill into the seafloor. Driving is a fast process, pile fabrication is relatively cheap, and soil conditions, consisting of firm sand and gravel, were suitable for piling. In close cooperation with the client, IHC made a driveability study with the help of the IHC-WAVE program. The driveability proved to be optimal with the S-600, with about 40 blows per 25 cm over the last few meters. The S-600 set has a blow energy of 600 kJ (600 kNm). Together with the fixed sleeve, the Hydrohammer has a total weight of 140 mt. The shipment included a water-cooled hydraulic powerpack, a control cabin, and winches mounted with hydraulic hoses and control cable.