‘Suction buckets’ could be wind developers’ solution to glauconite on the seafloor

‘Suction buckets’ could be wind developers’ solution to glauconite on the seafloor

An offshore wind developer will soon test-install a new type of turbine foundation — a suction bucket — in its lease area south of Martha’s Vineyard. Suction buckets may help wind developers build turbines amid difficult soil conditions, including glauconite — a tricky, sticky substance found along the Atlantic outer continental shelf. 

Beacon Wind received permission from the federal government this month to test a suction bucket at about 25 locations. Unlike monopiles — the tall, thin foundation bottom of most wind turbines — suction buckets are relatively short and wide. They don’t go as deep and are quieter to install than piles, minimizing sound impacts and allowing more flexibility amid global supply chain constraints. 

Beacon Wind is one of four offshore wind lease sites on the East Coast confirmed to have glauconite, The Light has reported. The purpose of testing suction buckets for the Beacon project, states BOEM, the federal regulator of offshore wind, is in part to “assess foundation feasibility, and refine foundation design,” given the site’s geological conditions.

“Glauconitic sands impose constraints on pile driving for monopile foundations, causing pile refusal,” said BOEM in a new report for Beacon Wind. “Suction bucket foundations require a shallower depth penetration than monopiles and use different installation methods that are less influenced by glauconite sands. Thus, developers could install suction bucket jackets in areas that have glauconitic sands at depths that may interfere with monopile installation.”

BP, the oil and gas company which now has full ownership of the Beacon Wind project (it was previously 50-50 with Equinor), did not confirm whether glauconite is factoring into its testing of suction buckets. 

“We have proposed the trial as a means to test the feasibility of suction bucket foundations as a possible design option to be considered, in addition to monopiles and others,” BP said in a statement in March. “If successful, this technology could help mitigate potential impacts to the surrounding marine environment.”

What’s a suction bucket?

Beacon Wind is ultimately looking at the feasibility of a suction bucket jacket foundation: a three- to four-legged structure with a bucket on each leg. While suction buckets on their own can be a less expensive alternative to monopiles, jacket foundations can be more expensive, as they require more steel. 

Credit: Kellen Riell / The New Bedford Light

Monopiles are installed with a hammer, but suction buckets are installed via suction. A pump attached to the bucket sucks water out, creating a pressure difference that pulls the foundation into the soil. To remove the bucket, water is pumped back in. 

Ryan Beemer, an engineering professor at UMass Dartmouth, noted some benefits of suction buckets relative to monopiles. 

Installation is quieter, “which is hopefully more friendly to marine animals,” Beemer said. Also, since suction buckets do not require a hammer for installation, they may make logistics easier and cheaper for wind developers’ vessels. That could help developers deal with a squeezed supply chain. 

BOEM, in its approval of the foundation testing, echoed Beemer’s points, stating suction bucket technology could “minimize underwater noise” and “allow for more flexibility around supply chain constraints.”

In response to questions from The Light, BOEM said glauconitic sands are “geohazards,” and that as part of its site investigation, Beacon Wind will assess “geohazards’ potential impacts to foundation installation.”

Asked if alternative turbine foundations will be required in certain areas due to the risk of pile refusal, the agency said Beacon Wind is analyzing different foundations, including monopiles, piled jackets, and suction bucket jackets.

“All of these foundation types are under consideration, and the results of the suction bucket test will be incorporated into the analysis,” the agency said by email. 

In a 2021 study comparing turbine foundations, BOEM identified suction buckets as having the “least noise-emitting activities.” In light of this, several environmental organizations have voiced support for the alternative foundation, with some terming them “quiet foundations.” 

“We are keen to support efforts that embody our definition of responsible development, such as the voluntary measures by Beacon Wind to incorporate technology that avoids some of the most harmful impacts of development: noise from pile-driving,” said several organizations, including the Conservation Law Foundation and Mass Audubon, in a letter to BOEM. 

Because pile driving creates significant underwater noise, developers must follow mitigation measures. They cannot pile-drive at night, or when marine mammals are spotted nearby, or during certain months — all of which can delay construction. 

“By far the most effective way to reduce noise during construction is to install quieter foundation types, such as the suction-bucket foundations,” the environmental groups wrote. “A transition to quiet foundations may ultimately provide developers with more flexibility (e.g., wider construction schedules, the possibility of installing foundations at night), at least in some areas, as an added benefit of avoiding noise generated from pile-driving.”

Map credit: Kellen Riell / The New Bedford Light, Datawrapper, OpenStreetMap. Leases identified with information obtained from BOEM at boem.maps.arcgis.com.

Still, alternative foundations bring tradeoffs and risks. 

“The suction buckets are a bit harder to design for, and you risk blowing out the internal soil plug and having reduced capacity if the installation goes wrong,” Beemer said. “So, higher installation risk in exchange for several benefits.”

The wind developer Ørsted installed the first suction bucket jacket for an offshore wind farm in 2014 in Germany. According to a 2020 report, monopiles accounted for about 81% of wind turbine foundations in European waters, essentially serving as the default unless site conditions are not amenable.

“There is limited industry experience in the design, fabrication and installation of [suction bucket jackets] compared to the more common [monopile] foundation solution,” reads an Ørsted report. “The installation process for [suction bucket jacket] structures is yet to become standard practice and is thus considerably more complicated in practice than the installation process of monopiles.”

The New England and Mid-Atlantic Fishery Management councils, in a letter to BOEM last year, said the Beacon Wind developer should explain whether suction bucket jacket foundations can be used in parts of the lease that are “unsuitable for monopiles … perhaps because of the presence of glauconite.”

“Given this foundation type is not in widespread use and has not been approved for any U.S. projects, will there be pilot testing of these structures?” the councils had asked. 

Beacon Wind’s construction and operations plan notes glauconite was detected in “deeper sediments” within the lease, and that if it is sufficient in concentration, it could affect how the soil behaves for construction. BP did not confirm how much glauconite is present and at what thickness, concentration and depths.

BP ran suction bucket testing at offshore wind sites overseas. Here in the U.S., the testing will last up to two weeks and ground-truth the feasibility of these little-used foundations. 

Email Anastasia E. Lennon at [email protected].

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