World firsts at Kaskasi

10 August 2022

Among innovations at RWE’s Kaskasi offshore wind farm in the German North Sea is the installation of collars designed to improve the structural integrity of monopile foundations.

Above: Collar installation at the Kaskasi offshore wind farm

For the first time ever, the special collars were installed at Kaskasi around three monopile foundations at seabed level. The ‘collared monopile’ is a design based on an RWE patent. The new technology will provide additional support for lateral loading, increase the bearing capacity and improve the structural integrity of the entire foundation, says RWE.

Installation works were carried out by DEME Offshore.

Sven Utermo¨hlen, CEO offshore wind, RWE Renewables said: “At our Kaskasi offshore wind farm we use innovative technologies that will set standards throughout the entire offshore industry...The collared monopile, a patented solution developed in-house, will help to increase stability in difficult ground.”

Kaskasi is RWE’s sixth wind farm off the German coast. The 342 MW facility is currently under construction 35 km north of the island of Heligoland.

The three foundation collars – each 7 m high and weighing 170 tons – were successfully embedded into the seabed.

The installation, in water depths of up to 25 m, was carried out by DEME Offshore’s jack-up vessel Sea Challenger.

The space between the collar and monopile foundation was filled with grout material, creating a stable connection.

RWE will carry out tests to verify that the collar improves the structural behaviour in comparison with standard monopiles.

The detailed design of the collars was developed by the German civil engineering company JBO, based on the RWE patent. Bladt Industries was selected as manufacturer and DEME Offshore was responsible for the transportation as well as installation.

For the installation of the three collars DEME Offshore developed a complex tailor-made set of procedures, including underwater cleaning of the monopiles and boat landing protection. For the embedment of the collars into the seabed, “plug and play ballast weight frames”, with a total weight of 1000 t, were designed and built. For the grout filling, remotely operated vehicles were empoloyed.

Further innovations introduced at Kaskasi include vibro pile driving technology and the ‘Self-Expanding Pile Shoe’, a new foundation technology with a concrete ring that expands in the seabed.

Siemens Gamesa and RWE are also equipping a number of the Kaskasi wind turbines with recyclable rotor blades. The blades are the first of a kind, employing an innovative resin that enables components to be recycled and used in new applications at the end of their lifecycle. Installation of wind turbines at Kaskasi is scheduled to start this summer and by the end of 2022 a total of 38 wind turbines should be fully operational.

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