Data centers are often pictured as a giant brains, but the miles of wires and cables radiating from them are more like tentacles. A single 500-acre hyperscale campus, like the one contractor Mortenson is building in Eagle Mountain City, Utah, has 40-plus miles of duct banks needed to securely house those lines.
Mortenson is among several companies that are re-thinking all the steps involved and has notched impressive safety improvements along the way with reduced hazard exposure from working in trenches.
Duct banks 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 duct banks are often built amid mud and trenches often need dewatering in bad weather -- extending the process to three to 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 labor intensive job unfolds, workers are exposed to slippery conditions, trench cave-ins and chemical burns from wet concrete.
Large large electrical contractors like Rosendin Electric and Bergelectric have looked at the problems related to duct banks. Utility contractors like excavation and utility contractor Muller and Contech Engineered Solutions and large general contactors and construction managers like DPR and Turner 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.
Data center developer QTS had hired Mortenson for the big Utah project.
"The idea spawned from the hyperscale Eagle Mountain data center," explains Nate Haack, BLUvera's 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 pounds 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 (per BLUvera internal tracking, 2024). The practice has cut trench exposure by 60-70%, according to a company case study of the Eagle Mountain project.) Crews cycle the same tasks daily in the fabrication shops. The work performed at the site is setting the 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, and cut down crane lifts by 60%. Only one lift is needed per 20 ft of duct bank versus 10 to 15 using a cast-in-place approach.
"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 down dramatically, too.
"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 their prefabrication concept a step further. It now deploys mobile factories near data center project sites.
These mobile factories, set up close to the work sites, 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 job site, then we'll move on to the next one."
Right now, Mortenson 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 is seeing with data centers and compares it to projects where 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 banks for a hospital -- another kind of electricity and data hungry structure.
The electrical contractor, Enterprise Solutions, "dug the hole on a Monday, pretty much excavated the entire hole in one week," he explains. "And in the next four weeks, they poured the concrete for the [duct bank] pedestals, set the banks, tied everything up and had it inspected. It was done in 30 days," but "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 Haack says will further reduce onsite labor by eliminating the need for anyone to be in the trench to glue the PVC conduit sections. And the new system will, he adds, reduce the work's carbon footprint by "north of 30%."
The unfolding data center building boom will provide plenty of opportunities to see what works best.