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Jan De Nul Group Excavates Foundation for Offshore Wind Farm

The backhoe dredge Gian Lorenzo Bernini will be used to excavate the foundation pit for the gravity based foundation.

The backhoe dredge Gian Lorenzo Bernini will be used to excavate the foundation pit for the gravity based foundation.

In mid-November 2016, and 50Hertz Transmission GmbH announced that they had awarded the Joint Venture Iemants-Jan De Nul Group the EPCI (Engineering, Procurement, Construction and Installation) contract for two gravity based foundations (GBFs). This will be part of the Kriegers Flak Offshore Wind Farm, a 600 MW offshore wind farm in the Danish Baltic Sea, together with the Combined Grid Solution interconnector project. As of December 2016, engineering for the project has been started.

The gravity based foundations will be constructed on a pontoon based in the Port of Zeebrugge, Belgium, and towed to the Baltic Sea. In Denmark, Jan De Nul’s backhoe dredge Gian Lorenzo Bernini and its brand-new multipurpose vessel Adhémar de Saint-Venant will take care of the excavation of the foundation pit and installation of the gravel bed.

The backhoe dredge Gian Lorenzo Bernini, built in 2014, is a relatively new addition to the Jan De Nul fleet. She has a 60 meter (197 feet) length overall and beam of 18 meters (59 feet) and a draught of just more than 3 meters (almost 10 feet). Her gross tonnage is 1321 tons with a bucket or grab capacity of 8.5 and 25 cubic meters (33 cubic yards) respectively. She can reached depths of 30 meters (98 feet).

The multipurpose vessel Adhémar de Saint-Venant, which was launched at the AVIC shipyard in Weihai, China, in March 2017, is equipped with dynamic positioning (DP2) to do trenching and subsea rock installation. She is able to do subsea rock installation through an inclined fall pipe or a flexible fall pipe; she also does subsea trenching, installation of cables and umbilicals, as well as installation works by means of a heave compensated deck crane. She has a fully dieselelectric machinery arrangement, accommodations for 60 persons and a Special Purpose Ships (SPS) notation. She is 95 meters (312 feet) long with a width of 22 meters (72 feet) and a loaded draft of 6.5 meters (21 feet). She is equipped with a remotely operated underwater vehicle (ROV) Trencher, a Workclass remotely operated underwater vehicle, and an A-Frame. The Adhémar de Saint-Venant also has a ‘Strength bottom’ class notation, which allows the vessel to be beached, enabling cable installation works in very shallow waters.

The wind farm consists of two sections, each with its own substation. Kriegers Flak A, the west section, will have a total capacity of 200 MW. The east section, Kriegers Flak B, will have a total capacity of 400 MW. The gravity based foundations will be installed offshore by the end of 2017. By 2022, Denmark’s largest offshore wind farm to date will start generating CO2-free electricity for approximately 600,000 households. The interconnector project is funded by the European Energy Program for Recovery.

Engineering was started in early December and the cement works are taking place in Zeebrugge (Belgium), with the offshore installation scheduled for June and later in the autumn of 2017.

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