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Ørsted’s experience with suction bucket jackets


Pioneering an alternative to monopile foundations


Ørsted has been an industry leader in the development of suction bucket jacket (SBJ) technology used for wind turbine foundations, having installed the world’s first SBJ for an offshore wind turbine generator (WTG) at the Borkum Riffgrund 1 offshore windfarm in Germany in 2014.

This page provides a very brief background to the use of SBJs as a foundation solution for wind turbine generators. It includes a brief description of SBJ application on wind farms, an assessment of the limitations of SBJs, and a summary of Ørsted’s experience with this technology.
The prevalence of the monopile foundation

The most commonly used offshore wind foundation is the monopile. At the end of 2019, 81% of offshore WTGs in European waters used monopiles (Wind Europe, 2020). Where site conditions do not allow for an efficient or practical monopile design, a number of alternative foundation solutions are available, including the SBJ.

While it is complicated to install monopiles, there is a high degree of experience with this foundation type in the offshore wind industry, so this complexity has become well understood and manageable in practice. By contrast, the installation process for SBJ structures is yet to become standard practice, making it considerably more complicated in practice than the installation process of monopiles.
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Suction bucket jackets in offshore wind applications

Wind turbine foundations installed by suction, variously referred to as suction buckets, suction caissons, suction piles or suction anchors, have been used widely in the offshore oil and gas industry since the early 1980s for a range of applications. These foundations, normally made from steel or concrete, are installed using the principle of suction, whereby the pressure difference generated between the inside of the bucket and the water surrounding it at the seabed leads allows the structure to be installed without the use of any mechanical force. A key difference between suction-installed foundations and other foundation types is that the installation design has to consider soil type, soil strength, and risks specific to the installation (for example, the presence of boulders or other hard inclusions).This, along with the installation process (for example, the speed of installation), has a direct influence on the dimensions of the foundation.

More recently, suction-installed foundations have been deployed in the offshore wind sector, with installations at Borkum Riffgrund 1 (2014; one position), Borkum Riffgrund 2 (2018; 20 positions) and Aberdeen Bay (2018; 11 positions). For this application, three suction buckets are used to support a ‘jacket’ structure, hence the name suction bucket jacket.

SBJs for windfarm applications differ significantly from typical oil and gas suction-assisted installations, such as suction anchors.

  • They are connected rigidly to a structure, such as a jacket.
  • They are installed in relatively shallow waters (less than 100m water depth).
  • They predominantly carry vertical loads (and relatively small moment and horizontal loads), which results in behaviour very similar to a shallow foundation.
  • They have a large overall footprint and a low length to diameter ratio, meaning that they generally cover a large spatial area whilst maintaining a small embedment into the soil.

Limitations of suction bucket jackets

SBJs have the following limitations in comparison with monopiles:

  • They have a significantly larger footprint (approximately 30-40 m in diameter) and require more scour protection.
  • Due to their shallow embedment, they cannot always be installed at locations with large sand waves or high seabed mobility.
  • There are installation challenges in shallow water (less than 20m).
  • The installation process is highly dependent on soil type and soil strength.
  • The installation process is potentially riskier due to the larger volume of soil in contact with the structure. That is, there is higher risk of ground variability, hitting a boulder or encountering a hard inclusion. There is currently a lack of proven mitigation options available.
  • Installation experience is limited in the offshore wind industry.
  • Manufacturing experience and scale is limited.
  • The overall cost may be higher.
Ørsted’s experience

Having installed the first SBJ foundation for a WTG at Borkum Riffgrund 1 in 2014, Ørsted is continuing to develop this technology, with the aim of providing flexibility to choose between a range of different wind base foundation options each new offshore wind project.

Since 2014, Ørsted has been involved in the design and installation of SBJs at Borkum Riffgrund 2. We were also involved in the design of SBJs for Hornsea 1. Here, overall project timeline considerations and limitations on serial production capacities meant that the project ultimately chose an alternative foundation type.
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Ørsted publications on suction bucket jackets

There is a significant volume of published literature relating to suction buckets, from early work in the context of offshore oil and gas (Bye et al, 1995 and Erbrich & Tjelta, 1999), through to more recent work on the offshore wind context (DTI, 2005, Houlsby and Byrne, 2005, Achmus et al, 2013, Tjelta, 2014 and Shonberg et al, 2017). The literature relates both to the installation of suction buckets and to their behaviour under different loading conditions. More recently, it has focused on the use of suction buckets for offshore wind applications.


References

The following publications relating to SBJs authored by Ørsted employees (or those directly associated with Ørsted) have been published:

Harte, M., Shonberg, A. (2018)
“Reliability based installation design of a suction caisson in clay”
Proceedings of the 1st Vietnam Symposium on Advances in Offshore Engineering (Energy and Geotechnics), 1-3 November 2018, Hanoi, Vietnam (submitted, under review)

Shonberg, A., Harte, M., Aghakouchak, A., Andrade, M.P., Brown, C.S.D., Liingaard, M.A. (2017) “Suction bucket jackets for offshore wind turbines: applications from in situ observations”,
Proceedings of the TC209 Workshop at the 19th International Conference on Soil Mechanics and Geotechnical Engineering, 20 September 2017. Seoul, South Korea.

Shonberg, A., Anusic, A., Harte, M., Schupp, J., Meissl, S., Liingaard, M. A (2017)
“Comparison of Self Weight Penetration Prediction Methods for Large Diameter Monopiles in North Sea Soils”, OTC-27763-MS. Proceedings of the Offshore Technology Conference, 2 – 5 May, 2017, Houston, Texas.

Surysentana, S., Byrne, B. W., Burd, H. J., Shonberg, A. (2017)
“Weighting functions for the stiffness of circular surface footings on multi-layered non-homogeneous elastic half-spaces under general loading”
Proceedings of the 19th International Conference on Soil Mechanics and Geotechnical Engineering, 17 - 21 September 2017, Seoul, South Korea.

Suryasentana, S., Dunne, H., Martin, C., Byrne, B. W., Burd, H. J., Shonberg, A. (2018)
“Assessment of numerical methods for determination of shallow foundation failure envelopes”, Geotechnique (submitted for review).

Surysentana, S., Byrne, B. W., Burd, H. J., Shonberg, A. (2017)
“An elastoplastic 1D Winkler model for suction caisson foundations under combined loading”
Proceedings of the 9th European Conference on Numerical Methods in Geotechnical Engineering (NUMGE), 25 - 27 June 2018, Porto, Portugal.

Surysentana, S., Byrne, B. W., Burd, H. J., Shonberg, A. (2017)
“Simplified model for the stiffness of suction caisson foundations under 6 DOF loading”
Proceedings of the SUT OSIG Conference, 12 - 14 September 2017, London, UK.

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Our experience with suction buckets

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