Deep foundations for an Offshore Windfarm – A challenge not only to dive-drill from seabed-Paper

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Bauer completed deep foundation work for the Saint-Brieuc offshore wind farm in October 2023. Located 16 km off Brittany, the 496 MW project comprises 62 turbines and an offshore substation. Its jackets are supported by 190 steel piles installed in drilled boreholes and secured with grout—an innovative approach and the first use of drilled and grouted steel piles for an offshore wind farm.

The work was carried out from Van Oord’s vessel <em>Aeolus</em> in challenging Atlantic conditions, with water depths of 29–42 m. Unexpectedly strong, abrasive and clog-prone ground differed from tender assumptions, causing drilling difficulties and increased tool wear. Bauer adapted its equipment and methods during construction, including developing the purpose-built “Dive Drill,” changing from auger tools to full-face cutters in competent rock, and improving flushing to remove excavated material.

Precise pile positioning and installation required extensive above- and underwater monitoring. Systems measured depth, inclination, position and grout level, while process data were recorded to support quality control and as-built documentation.

Grout had to fill the annular space reliably, remain workable during installation and provide durable load transfer. After extensive laboratory, approval and full-scale testing, two seawater-based cement grout mixes were qualified. More than 10,000 m of grout was injected successfully.

The project’s completion depended on adapting to actual ground conditions, developing specialized equipment, maintaining accurate monitoring, and coordinating closely among Bauer, Ailes Marines, Van Oord and DNV.

Keywords

Saint-Brieuc offshore wind farm

deep foundation

offshore wind

drilled and grouted steel piles

Bauer

Brittany

grout injection

Aeolus vessel

pile installation

ground conditions