Installation of Suction Caissons
- Precedent Consultants
- Apr 1
- 6 min read
At Precedent Consultants, we focus on reducing risks for Clients. This involves several foundation solutions, such as the installation of offshore suction caissons.
Firstly, what are suction caissons? Suction caissons or suction buckets have been used offshore for many years to support infrastructure. These structures have historically been found in oil and gas facilities, specifically used as anchors for a variety of structures, including those at seabed level and as foundations for tension leg platforms. In offshore wind, after several demonstration platforms and substations were successfully deployed and the technology had proven to demonstrate that it actually works, the market gradually, then collectively jumped at the opportunity to install these structures. Some of the most recent projects using suction caissons to support offshore wind include the following:
Borkum Riffgrund 2 OWF, completed in 2018 with 20 WTGs
Aberdeen OWF, completed in 2018, with 11 No. WTGs
Fujian Changle Waihai Area (East China Sea) OWF, completed in 2021, with 72 WTGs
Seagreen OWF, completed in 2023 with 114 WTGs
Greater Changua b OWF, completed in 2025 with 24 WTGs
Why Suction Caissons?
Offshore wind was pioneered in Europe, but the technology has spread worldwide. Shallow water depths, thick layers of dense sands, and over-consolidated clays facilitated monopile designs. As the industry now moves into other territories in deeper waters or into regions with unexplored soils or shallow bedrock, it faces new and different challenges. By capitalising on suction caisson technology, the shallow soil layers overlying the bedrock can be used to support offshore wind.
The protection of the offshore wildlife is critical to future generations. In several jurisdictions, noise levels from offshore operations need to be mitigated. Whereas pile driving creates high noise levels, caisson installation is comparatively quiet. Instead of continuously hammering piles using metal tonnage, suction pumps are used to remove the water from within the caissons, facilitating installation.
Additionally, at locations with shallow rock, the cost and risk associated with offshore drilling are high, whereas the installation of suction caissons is relatively short. There can also be significant cost savings from using suction caisson technology if adequate investigations and robust engineering are conducted prior to fabrication and installation.
After several discussions, there still seems to be a collective few who do not understand the suction caisson technology, and some who are reluctant to use this technology, potentially due to a lack of awareness of the great strides that have been undertaken over the last few years to reduce the installation risk.
Caisson Installation
Now, caisson design is geotechnically divided into two main areas. This includes getting the caissons in (installation) and, once in, withstanding the design loads (design). Regarding installation, the short graphic illustrates the caisson installation process.
This is shown as an example of a caisson supporting a WTG on a 3 or 4-legged jacket structure. As can be noted, there are several stages involved in the installation. These include:
The jackets with the caissons are lowered to the seabed. The weight of the structure and caissons is to be large enough to cause self-weight penetration. This self-weight penetration fundamentally needs to be sufficient to form a seal.
Once the seal is formed, suction can be carefully applied.
The suction force that is readily available is dependent on a number of factors, including the caisson diameter.
The water depth is a limitation, as the amount of suction that can be applied, depends on this.
There are then limits to the suction pressure that can be applied. Considerations on the prevention of plug collapse (geotechnical) and buckling (structural) necessitate a strong working relationship between the engineering teams for a successful design.
The suction is required to push the caisson skirts through the soil until achieving the target penetration.
There is a careful balancing act that is needed between the two design conditions that influence the skirt thickness. The larger the thickness, the more suction pressure that is needed; the smaller the thickness, the more susceptible the caisson is to buckling.
Once arriving at the intended target depths, the void atop the caissons is filled with grout and scour protection applied.
There are various methods currently available for estimating the suction pressure (or underpressure) required to install suction caissons. These include:
DNV-RP-C212 (2021)
Houlsby and Byrne (2005a & 2005b)
Andersen et al. (2008)
Both the Houlsby & Byrne and Andersen methods are developed based on first principles. The DNV-RP-C212 (2021) approach applies factors to measured CPT data and has seen much progress due to its simplicity. Here, tip resistance factors, kp and skin friction factors kf are applied to the measured CPT tip resistance qc. The total resistance of the caisson at a given depth is then determined based on the sum of the bearing resistance of the skirt tip and the integral of the shaft resistance over the current penetration depth. For a caisson penetration of depth z, the total soil installation resistance Rtotal is calculated by the empirical relationship:
where Ashell represents the internal and external skirt area per unit depth (m²/m), and Atip is the area of the annulus (m²).
The factors in DNV-RP-C212 (2021) can be used to provide initial resistance estimates of penetration resistance due to suction. However, based on locality, more calibrated factors may be used. The following are based on approaches developed for over-consolidated soils in the North Sea and those in the East China Sea, effectively creating a modified series of factors for the DNV approach. The DNV factors are provided for context.
DNV Factors – DNV-RP-C212 (2021)
North Sea – Joseph et al (2023) - Click to access paper
East China Sea – Brandolini et al. (2025)
(The industry does need to have more data published – if available, please share!)
As observed, the resistance factors can then be assigned according to the soil types. The suction caisson installation resistance can then be estimated from caisson properties to achieve the target penetration. However, not all caissons readily reach their intended target penetration. The following are potential causes of refusal, aka no longer moving downwards:
Excessive tilt
Piping
Presence of boulders
Plug uplift
Fluidisation of the plug
De-risking Caisson Installation
To de-risk the installation operation, mitigation measures are deployed. These are usually separated into two categories: pre-emptive and reactive. Pre-emptive methods are considered during design. These would include methods such as reducing the caisson skirt length or reducing wall thickness. Reactive methods are applied during installation, which include:
One-Way Cycling: Pausing the application of suction, then starting either immediately or after a specific rest time.
Two-Way Cycling: This process involves stopping the suction (underpressure to cause downward motion) and applying a reverse suction pressure (overpressure) to create upward motion of the caisson. However, this approach must be progressed with caution due to the detrimental effects that can be caused on the integrity of the geotechnical caisson design.
Micro-siting: This process involves the relocation of the suction bucket jacket to a nearby position if refusal in encountered.
Ballasting (increased deadweight), is not considered very effective due to the quantity of weight that would be required to see any real penetration progress. This process would also need to be factored into the design to allow implementation if caisson refusal occurs.
The Precedent Advantage
Offshore wind projects typically take 7 to 11 years from idea to operation. Throughout this lengthy process, Precedent Consultants can serve as your Technical Advisor. We are not experts in all engineering disciplines, but via our network can assist in several areas. Our multidisciplinary approach combines technical expertise in geological and geotechnical engineering with risk assessment to ensure your project is both financially viable and robust.
Whether you're in the initial feasibility phases or optimising an operational asset, our experts are here to assist. Time to set a precedent? Please reach out as we have the key expertise in this field. Visit www.precedentconsultants.com to learn more about our services or to schedule a call to discuss your project needs.
Key references
Andersen, K.H., Jostad, H.P. and Dyvik, R., 2008. Penetration resistance of offshore skirted foundations and anchors in dense sand. Journal of geotechnical and geoenvironmental engineering, 134(1), pp.106-116.
DNV, 2021, "Offshore soil mechanics and geotechnical engineering," Recommended Practice DNV-RP-C212, September 2019 (Amended September 2021), DNV AS, Oslo, Norway.
Houlsby, G.T. and Byrne, B.W., 2005a. Design procedures for installation of suction caissons in sand. Proceedings of the Institution of Civil Engineers-Geotechnical Engineering, 158(3), pp.135-144.
Houlsby, G.T. and Byrne, B.W., 2005b. Design procedures for installation of suction caissons in clay and other materials. Proceedings of the Institution of Civil Engineers-Geotechnical Engineering, 158(2), pp.75-82.
Joseph, T., Mallikarachchi, H., Gütz, P., Hamdan, N., Powell, T. and Jones, L., 2023, September. Mitigation of Suction Caisson Installation Refusal by Two-Way Cycling–Part I. In SUT Offshore Site Investigation and Geotechnics (pp. SUT-OSIG). SUT.
Zuccarino, L., Brandolini, C., Piatti, C. and Gioffrè, D., 2024, June. New Site Specific CPT-based Suction Bucket Jacket Installation Coefficients from Field Measurements. In ISOPE International Ocean and Polar Engineering Conference (pp. ISOPE-I). ISOPE.
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