Situated some 12km off the Loire-Atlantique coast of France in water depths ranging from 10.0 m to 25.0 m Lowest Astronomical Tide (LAT), the Saint-Nazaire offshore wind farm will comprise 80nr 6MW GE Haliade 150 turbines spread over an area of 78km2, and is expected to power 20% of the Loire-Atlantique department.
Fugro performed the first geotechnical survey campaigns on the site in 2011, 2013 and 2015 surveying half the wind turbine positions and taking soil/rock samples. Those previous experiences on site allows Fugro to acquire a detailed knowledge of the site condition and propose for the 2018 campaign the best technical solutions adapted to the challenging geology that had been previously identified.
Thanks to Fugro varied and extensive resources, the work could be undertaken by two offshore spreads, the jack-up barge Excalibur and the Fugro Scout drill ship, between 25 May and 27 June 2018. The use of two different spreads allowed the work to progress simultaneously in different ranges of water depths and the program to be performed with maximum time efficiency. Taking advantage of the summer period was a key point for this project.
Drilling operations on both marine spreads were performed using the Geobor S system. Drilling operations and quality of the core samples recovered confirmed the efficiency of the system observed during the previous campaign in these types of soil and rock conditions. In addition, in-situ tests were performed: CPT on sediment layers and downhole geophysical logging along boreholes.
To meet the ambitious schedule a team of eight geologists and geotechnical specialists worked onshore on the geological and geotechnical data at a specialist laboratory at Boussens in the South of France, some 60kms from Toulouse. The project began on schedule in May 2018 with all field activities completed by August 2018, with consultancy reports submitted in regular stages to PBG.
The majority of the soil and rock testing was performed by experienced personnel at the Fugro laboratory in Nanterre, France (close to Paris); they had worked on testing for the first campaign in 2013, which provided them with considerable expertise for dealing with all that was needed in 2018. From July onward, they undertook a huge amount of testing of soil and rock samples including hundreds of unconfined compressive strength tests; point load tests; triaxial tests; and resonant column, classification and compression tests. Additional soil tests were also performed at Fugro’s UK laboratory in Wallingford, UK.
During this project Fugro laboratories have provided the project with the following benefits:
As two laboratories were involved in the testing, Fugro was able to provide a quick turnaround on testing large volumes of samples.
Fugro has now worked on more than 120 offshore wind farm sites globally, and is able to cover all project elements from feasibility studies, geotechnical investigations and surveys, design, installation and commissioning. In France, Fugro has already been working on 6 of the 7 offshore windfarms under development and is also actively involved in the new challenge of the floating windmills.
Fugro has worked on more than 120 offshore wind projects across the globe. By early 2020 these projects are estimated to have a total capacity of 30GW.