German construction and machinery manufacturing firm Bauer Spezialtiefbau has tested onshore piles at the Saint-Brieuc offshore wind project in France to gather data for the design of foundations.
The engineering outfit 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 of the onshore tests was to obtain important friction values for the foundation of the planned offshore wind farm,” explained 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,” he added.
The test piles were installed in an active quarry near Cap Frehel in Brittany.
Niklas Haag, project manager at Bauer Spezialtiefbau, said: “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."