First hammer blow in the North Sea

Construction of the Trianel Borkum wind farm begins


Borkum/Aachen. “Following three years of project development, today the construction ship will cast off”, explains Klaus Horstick, Managing Director of Trianel Windpark Borkum (TWB), with obvious satisfaction.

From today, the jack-up ship Goliath will be used at a site 45 kilometres off the coast of Borkum to fasten the first steel pipes of the foundation structures at a depth of around 30 metres below water. 

“The construction site logistics at sea present a completely different challenge to that of a power station site on land”, comments Horstick. The 160 metre high wind turbines of the Areva M 5000 type stand on enormous three-legged foundations, the so-called tripods. The 700 tonnes heavy tripod foundation structures, which are currently being manufactured at the Tripod Borkum West II consortium (Weserwind/EEW) in Bremerhaven, will be anchored to the seabed using three hollow 100 tonnes heavy steel pipes, the so-called piles.

Preparatory work for the first communal offshore wind farm started back in spring – the first step being the preparation of nature protection measures. The large bubble curtain which is inserted around the construction site as protection for marine mammals was tested on land. Then in August the first tests took place at sea. The objective of the bubble curtain is to protect primarily the porpoises from the noise which is created during the pile driving work for the foundations. 

“The procedure at sea has been planned in great detail”, explains Horstick: “The boat with the bubble curtain will sail to the planned foundation position in order to insert the bubble curtain around the construction site.” Once the bubble curtain has been completed around the construction site, which has a diameter of about 100 metres, the Goliath will sail inside the sound-protected area. There, the ship will hydraulically lower its four outriggers to the seabed to position itself. “With its jack-up legs the Goliath is firmly installed on the seabed”, explains Klaus Horstick.

Then a ramming template will be placed on the seabed and each pile is rammed down with up to 3,000 impacts from the hydraulic hammer, with accuracy to within the nearest millimetre. The template is necessary in order to ensure that the steel tubes are placed at the correct distance from each other so that next spring the tripods can be lifted on to the piles. 

The piles have a diameter of 2.5 metres and are 25 to 30 metres long. Longer or shorter piles are used depending on the composition of the soil. “The soil substrate has been analysed in detail by geologists so that we know exactly where we have to use piles of a certain length”, reports Horstick.

The final installation of the 40 wind turbines of the first construction phase will begin in the summer of 2012 and is scheduled for completion in the winter of 2012/13. TWB intends to supply power at that time. The second TWB construction phase with a further 40 wind turbines is scheduled for 2014. The preparations for this second phase are already in full swing. And furthermore, the group of public utility companies is already thinking about follow-up projects to Borkum West II. 

Elmar Thyen
Head of Communications
Tel +49 (0)241 41 32 04 13
Mobile +49 (0)151 12 64 17 87

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