In France, the use of offshore wind energy is still in its infancy. However, this is set to change over the next few years. According to a report by the
International Economic Forum for Renewable Energy (IWR), the French government plans to build offshore wind farms with a total output of more than 5,000 MW by 2030.
One of these projects is an offshore wind farm in the Bay of Saint-Brieuc in northwestern France, slated for construction in 2021/22. The contract for constructing, installing and operating the wind farm was awarded to Ailes Marines SAS, in which Iberdrola (70%) and Avel Vor (30%) have a stake. Based in Bilbao, Spain, Iberdrola is one of Europe's five largest energy suppliers and a world leader in wind energy.
Bauer Spezialtiefbau GmbH was contracted to design and install a total of 14 onshore test piles, including load testing, for the planned wind farm. “The aim of the onshore tests was to obtain important friction values for the foundation of the planned offshore wind farm,” explains Paul Scheller, head of Underwater Foundations at Bauer Spezialtiefbau. “This will be the first commercial application for this type of piles worldwide. Bauer has
developed a special drilling system for such projects in order to install temporary cased drilled and grouted piles offshore in a variety of different types of subsoil.”
The test piles were installed in an active quarry near Cap Frehel in Brittany. Niklas Haag, Project Manager at Bauer Spezialtiefbau, reports: “The biggest challenge was the ultra hard rock. During all three exploratory drilling operations, we encountered rock with strengths exceeding 180 MPa. That's 60 MPa more than originally foreseen in the contract. Anyone familiar with the subject knows that drilling in such hard rock is extremely demanding. As a result, drilling the 1,350 mm diameter piles took much longer than expected and resulted in excessive wear on the roller bit core barrels that were used. However, in the end we completed the test drilling successfully, thanks to the tireless efforts of the Bauer team on site and the support by our colleagues in Schrobenhausen.”
Each borehole was measured using laser scanners from the Technical Services Department of Bauer Spezialtiefbau. The extreme test load of 10 MN was applied to the micropiles using a specially developed load distribution system. The larger piles were stressed with loads up to 40 MN using internal pile test jacks (Osterberg cells). Andreas Simson, head of testing at the Technical Services Department, used a geo-laser system to record the uplift around the test piles, recording the movement every ten seconds.
Pedro Barbosa, project manager at Iberdrola, was very satisfied with the successful tests, for which a Bauer BG 30 and a Klemm 806 2D were used. He thanked the Bauer crew for their extraordinary dedication: "Your efforts went above and beyond expectations," said Pedro Barbosa. Paul Scheller also had nothing but praise for the team: "This project would never have gone so smoothly without the excellent teamwork of everyone involved."