Duct bank sections are a series of conduits through which cables are routed. Traditionally, they are created by digging a trench, preparing the trench base, building forms and installing conduit cages before pouring concrete. The sections are often built in thick mud, and trenches often need dewatering in bad weather—extending the installation process to three or four weeks per 1,000 feet. The process is repeated over and over until the cables can be pulled through and the data center is powered up and connected. 

As the labor intensive job unfolds, workers are exposed to slippery conditions, trench cave-ins and chemical burns from wet concrete.

Large electrical contractors such as Rosendin Electric and Bergelectric have looked at the problems related to duct bank. Excavation and utility contractors such as Muller and Contech Engineered Solutions and large general contractors and construction managers such as DPR and Turner Construction also have duct bank programs or special methods.

Minneapolis-based Mortenson, through its manufacturing arm, BLUvera, took up the problems in 2020, opting to embrace precasting and large-scale off-site prefabrication.

“The idea spawned from the hyperscale Eagle Mountain data center,” explains Nate Haack, BLUvera vice president and general manager. “The project team was facing schedule challenges in a congested area—so they asked, ‘what if we precast these elements off-site and install them like Lego blocks?’”

Over the past five years BLUvera has scaled up its operation to produce modular 20-ft sections weighing 17,000 lb in off-site fabrication shops, slashing the onsite work hours by 56%.

Safety hazards for the workers have been slashed as well. Mortenson says it has seen an 87% reduction in safety incidents after switching to precast, according to 2024 BLUvera internal tracking data. The practice has cut trench exposure by 60 to 70%, according to a company case study of the Eagle Mountain project. Crews cycle the same tasks daily in the fabrication shops. Work performed at the site is setting duct bank beams and connecting conduits to each other.

Mortenson’s off-site pre-casting has reduced wet concrete exposure, eliminating possible burns, slips or form collapses. 

The process of building data center duct bank has been refined by Mortenson and includes placing concrete in an indoor fabrication shop. Photo: Courtesy of Mortenson.

“In the factory setting,” Haack explains, “we're under a roof, in a controlled environment with forklift lanes and truck lanes. The way that we pour our precast duct bank gets cycled every day. So for our team members, it's a rinse and repeat. Every day, they're doing the same task, because they're pulling every formwork every day.”

Defects are also down dramatically.

“We very rarely have one,” Haack says. “We have seen an 83% reduction in quality defects with the most common defect deriving from damage due to loading and unloading of the truck.”

To minimize transport costs and logistics, BLUvera took its prefabrication concept a step further, and now deploys mobile factories near data center project sites. Set up close to the work sites, these can be scaled up very quickly. 

"It’s very ineffective from a cost perspective to ship” duct bank sections, Haack says. “We sign a lease, take possession, and within a month we’re producing ... once we're done producing the products for the jobsite, then we'll move on to the next one."

Mortenson currently has a mobile duct bank factory in Louisiana. "We've been there since January and we'll be there for another year," says Haack. The company is working on leases for two more mobile factories.

Marty Corrado, a retired project manager, advocate for prefabrication and author of a prefabrication book, likes what he sees with data centers and compares it to projects on which he was involved.

 In 2017, working as a general superintendent for J.E. Dunn on the Sarah Cannon Hospital addition in Plano Texas, Corrado’s team included an electrical contractor's prefabricated duct bank for a hospital—another kind of electricity and data hungry structure. 

Eliminating as much labor as possible in trenches is one of the goals Mortenson says has improved safety performance significantly during duct bank construction. Photo: Courtesy of Mortenson.
   

Nashville-based Electrical contractor Enterprise Solutions "dug the hole on a Monday and pretty much excavated the entire hole in one week,” he explains. “In the next four weeks, [the team] poured the concrete for the [duct bank] pedestals, set the bank, tied everything up and had it inspected. It was done in 30 days," Corrado notes, adding that "this would typically take us four to five months.”

About Mortenson’s innovation, Corrado says he’s “so glad to see that the electric side of the industry is really starting to take to working efficiently.”

Haack says that Mortenson has more innovations in the works. It is preparing a new duct bank that he says will further reduce onsite labor by eliminating the need for anyone to be in the trench to glue the PVC conduit sections. The new system will reduce the project carbon footprint by “north of 30%,” he adds.

The unfolding data center building boom will provide plenty of opportunities to see what works best.