Bauer Spezialtiefbau has tested onshore piles at the Saint-Brieuc offshore wind project in France to gather data for the design of foundations.
Bauer Spezialtiefbau designed, installed and tested a total of 14 drilled and grouted piles at the Routin Quarry near Cap Fréhel, Brittany, under a contract signed with project developer Ailes Marines last year.
“The aim was to obtain important friction values for the foundation of the planned offshore wind farm,” said 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 German company said the piles were installed into very hard bedrock, a red sandstone formation which is also expected in parts of the future wind farm area.
Each borehole was measured using laser scanners. The extreme test load of 10MN was applied to the micro piles using a specially developed load distribution system, Bauer said.
The larger piles were stressed with loads up to 40MN using bidirectional internal pile test jacks, while a geo-laser system was used to record the uplift around the test piles, recording the movement every ten seconds.
“The biggest challenge was the extremely hard rock. During all three exploratory drilling operations we encountered rock with strengths exceeding 180 MPa, 60 MPa more than originally foreseen. Drilling in such hard rock is extremely demanding,” said Niklas Haag , Project Manager at Bauer Spezialtiefbau.
“It took longer than planned to drill the 1’350 mm diameter piles took and resulted in excessive wear on the roller bit core barrels that were used. However, in the end Bauer completed the test drilling successfully, thanks to the tireless efforts of the Bauer team on site and the support by our colleagues in Schrobenhausen.”
The Saint-Brieuc project will comprise 62 Siemens Gamesa 8MW turbines mounted on jacket foundations some 16km off the coast at the nearest point.
Ailes Marines, a joint venture of Iberdrola, RES, and Caisse des Dépôts, plans to have the 496MW offshore wind farm operational by 2023.