Suction bucket jacket: Development and case study

Following the comparison and contrast of suction bucket jacket (SBJ) and other types of foundations, this article focuses on Borkum Riffgrund 1, the first wind farm employing SBJ, examining the historical and geographical context of the attempt and development afterwards.
 

Origin

The concept of SBJ was co-developed by DONG Energy (now Ørsted) and Offshore Wind Accelerator (OWA) led by the Carbon Trust. The OWA is a program aiming to reduce construction costs of offshore wind farms, with researching scope covering cable laying, power system, underwater foundation, maintenance, operation, wind resource utilization, and the wake effect.

Back then, monopile underwater foundation was the most prevalence structure. In order to install underwater foundations in regions with strict restrictions on noise pollution, SPT Offshore introduced suction bucket foundation for offshore wind turbines on the foundations innovation competition launched by OWA in 2011. The application was tested in an Ørsted wind farm. Long been practiced in offshore oil and natural gas industry since the 90s, the technology had never been used for offshore wind underwater foundation. The technology won SPT Offshore the title as one of the four winners of the competition.
 

Debut

Borkum Riffgrund 1 is the first SBJ wind farm, located 38 km off the shore of Northern Germany, where the seabed is composed of dense and medium dense sandy soil, and siltier sand three to six meter under the sea. Such condition is ideal for experimenting the SBJ technology. Borkum Riffgrund 1 spans a 36 km2 area, consisting of 78 4-MW wind turbines from Siemens Gamesa, among which one deploys SBJ, while the rest use monopile underwater foundations. Co-designed by Danish engineering consultancy company, Ramboll, and the Norwegian Geotechnical Institution (NGI), the SBJ underwater foundation was accredited by the DNV to work 20-60m of optimal water depth. It weighs 850 MT, including three caissons welded on the jackets for easier transportation and installation.

The procedures of installing an SBJ is as followed:

After the underwater foundation is placed on the seabed, pumps in the three caissons start to pump out water in the caissons to reduce pressures within. The weight and differential pressure of a caisson insert the pipe to the seabed. A foundation can be firmly installed just 8m under the sea. Once caissons are in position, pumps will be recycled, and cement grouted between caissons and the seabed. For more details, refer to the last article.

GeoSea, subsidiary of Belgian company, DEME, was in charge of transportation and installation. SPT Offshore dealt with water-pumping for caissons. The two companies jointly put together the first SBJ underwater foundation of the world.
 

Developments

The world’s first SBJ is equipped with various sensors designed by the NGI, including strain gauge, temperature and pressure sensors, inclinometer, etc. Since the installation in 2014, these sensors have been collecting data, documenting changes of underwater foundation structure and soil condition during installation and operation, and thus help improve the SBJ technology.

With experiences from building Borkum Riffgrund 1, the world brought forward two other wind farms employing SBJ in 2018, Borkum Riffgrund 2 next to Borkum Riffgrund 1 and Aberdeen Bay of the U.K.

Borkum Riffgrund 2 is located 54km off the shore and has 56 8-MW wind turbines from MHI Vistas, with 20 of them using SBJ underwater foundations and types of sensors monitoring caissons. It has by far adopted the most SBJ underwater foundations in the world.
Aberdeen Bay has the highest SBJ utilization ratio, with its 11 8.4-MW MHI Vistas turbines all using SBJ underwater foundations.

In 2019, the Carbon Trust published “Suction Installed Caisson Foundation Design Guidelines,” illustrating key factors to be noted when installing SBJ underwater foundations, hoping to lower the threshold and accelerate inspections.
 

Conclusion

Together, Ørsted and the Carbon Trust took SBJ from oil and natural gas industry to offshore wind industry, expecting to reduce costs of installing underwater foundations, accelerate the process, and mitigate noise pollution and environmental damages. So far, SBJ posts fair performance, with continuous collection of operating data. Still, relevant experiences are much less than monopile or piled jacket underwater foundations.

For now, it is still uncertain whether soils of Taiwan is optimal for SBJ application. Off the shore of Changhua County, wpd bids for Datian abd Youde wind farms, saying soil condition there is not fitted for SBJ, disagreeing with Ørsted’s point of view. Environmental Impact Assessment Committee expect more detailed pros and cons analysis from wpd, to further clarify the feasibility of SBJ technology in Taiwan.
 

Sources

Our experience with suction bucket jackets. (2018). Ørsted. https://orsted.com/en/our-business/offshore-wind/wind-technology/suction-bucket-jacket-foundations
T., Shonberg, A., Harte, M., Aghakouchak, A., Brown, C. S. D., Andrade, M. P., & Liingaard, M. A. (2017). Suction bucket jackets for offshore wind turbines: applications from in situ observations. Proceedings of TC 209 Workshop 19th ICSMGE - Seoul, 20 September 2019, 65–77. https://www.issmge.org/filemanager/technical_committee_pages/16/Proceedings_of_TC209_Workshop.pdf
The Carbon Trust. (2022). The Carbon Trust. https://www.carbontrust.com/zh/node/991