Category: Renewable Energy
Client: DEME Offshore
Location: Saint-Nazaire Offshore Wind Farm, France
Image source : DEME Offshore/Illustration https://www.offshorewind.biz/2022/05/31/all-foundations-installed-at-saint-nazaire-offshore-wind-farm/
The project
G-Octopus were engaged by DEME Offshore to provide Pile Driving Monitoring (PDM) services during the installation of the monopiles of France’s first offshore wind farm, located offshore Saint Nazaire. The Saint-Nazaire wind farm aimed for a total capacity of 480 MW or the equivalent of 20% of the French department, Loire-Atlantique’s electricity needs. The foundations installation started in spring 2021 and ended in 2022.
Our challenge
Industry-first technology was deployed to install the foundations in solid rock and to enhance operational working time. A unique equipment deployed at Saint-Nazaire is DEME’s MODIGA, which encapsulates the piling operations (drilling, piling and grouting), protecting them from the weather conditions and thus increasing operational working time. The operations were carried out from the jack-up installation vessel ‘
Our solution
G-Octopus selected appropriate equipment and adapted operational procedure to produce a tailor-made solution. G-Octopus’ onshore teams installed the sensors and cables on the monopiles, and its offshore teams monitored the foundations installation.
To limit the impact of monitoring activity on the long term, the monopiles were cleaned from the sensors cables right at the end of the driving, with a specific release setting implemented at time of installation of the sensors.
In addition to the twelve instrumented monopiles, G-Octopus carried out back-analysis for twenty-five non-instrumented monopiles (both driven and hybrid). This method, allowed for the determination of the SRD of the non-instrumented monopiles, based on hammer log, correlations determined with the results of the instrumented monopiles and 1D wave equation analyses.
The impact
G-Octopus successfully understood and anticipated the issues that could occur during the installation of the monopiles and proposed a driving monitoring procedure which allowed activities to occur smoothly, whilst minimising time impact.
Pile driving monitoring was successfully performed for all instrumented monopiles, with a very limited data loss; this was thanks to equipment quality, selected redundancy, adequate cable management procedure, and good cooperation with the DEME team.
A short term restrike was also successfully performed at DEME’s request.
of the non-instrumented monopiles were carried out smoothly from our head office, as a result of good communication between client and offshore team.
Image source : La Rochelle port taken by a member of the G-Octopus team
Services Included:
- Pile Driving Monitoring
- Analysis of the pile axial capacity at the end of driving and at restrike
- Back-analysis of non-instrumented piles
Monopile Information:
- Diameter: 7m at sensors level
- Thickness: variable from 85mm to 100mm at sensors level
- Length below seabed: variable from 26m to 32m
Equipment Used:
- In-house underwater strain gauges
- In-house underwater Piezo-Resistive (PR) accelerometers
- PDM cables
- Pile Driving Analyser (PDA-S)
- GRLWEAP® software
- OPILE software (edited and manufactured by Cathie Group)
- CAPWAP® software