Water Infrastructure
Diver-Operated Vehicle Installs New Water Tunnel Liners Without Dewatering
After being lowered into a tunnel, BURT installs concrete liners underwater.
A project nearing completion in the Detroit area used a custom-built, diver-operated vehicle that can operate underwater and that replaced concrete liners for two raw water tunnels, eliminating the need for dewatering and diversion or prolonged outages.
The diver‑operated liner plate installation vehicle is a modular, 25‑ft‑long electric‑over‑hydraulic transporter dubbed BURT, for Ballard’s Underwater Ring Transporter. Ballard Marine Construction, part of the Traylor Construction Group, led a team that developed and tested BURT on land and at the O.H. Hinsdale Wave Research Laboratory at Oregon State University before deploying it in 2022 on a 12‑ft-dia unreinforced cast‑in‑place concrete tunnel built in the 1930s and one 10‑ft-dia tunnel from the 1950s. The tunnels both have precast primary segments and a secondary unreinforced lining, and are owned by the Great Lakes Water Authority.
Video courtesy Ballard Marine Construction
BURT completed the liner installations last fall, after three years of October-to-April windows for construction. The approximately $90-million progressive design-build project is slated to complete this spring with final grouting operations.
"We originally were going to go design-bid-build," says Todd King, chief resiliency officer with GLWA. "We would have dewatered the tunnels, take the treatment plant out of service, and do it piecemeal." But after learning of the potential to avoid that, the agency pivoted to PDB.
The tunnels sit about 95 ft below grade in soft clays and silts. Inspections had found cracking that was severe enough that a loss of pressure inside the tunnel posed a structural risk, notes Shawn Drobny, Ballard lead engineer.
Ballard worked with Kelley Engineered Equipment to develop BURT. "They said, we have this interesting problem—we want to try and reline this tunnel without draining the water out of it," recalls Matt Short, Kelley project engineer. The team brought in the Norwegian firm Innova, which specializes in solutions for high-voltage underwater hydraulic machines.
"It’s basically a forklift—but operating underwater with humans around it," says Short. "How do you make a toaster safe underwater? We did a back and forth with them on how to protect BURT with a line insulation monitor. On the hydraulic side, how do we keep it at a higher pressure so water doesn’t get into the machine?"
Photo courtesy Ballard Marine Construction
On site, BURT was lowered via an 8‑ft‑dia access shaft and reassembled on the invert 95 ft deep. "The water in winter hovers around 33° F," notes Drobny. "The divers were 1,800 ft from the repair sites with limited timeframes." Crews built tents over the access shafts and heated them, he says.
A Deep Dive
A Ballard-authored technical overview co-written by Drobny describes the process. BURT’s main body houses a deep‑sea hydraulic power unit with a custom bladder accumulator, a programmable logic‑controlled electrical system sealed in a nitrogen‑filled canister, and an onboard reel with more than 1,100 ft of 3/4-in. umbilical cord to power and communicate from the surface, says Drobny.
Four independently-driven hydraulic wheels provide positive traction; the system can hydraulically “lock” the drives so the 20,000‑lb vehicle is safely secured during peak flows. Two onboard cameras and eight LED lights feed twin underwater monitors at the operator’s station. "The underwater cameras and monitors for divers were critical to our success," says Drobny.
Video courtesy Ballard Marine Construction
A bright orange pre‑installed cable centerline on the tunnel invert enables navigation to within a half‑inch to avoid contact between the liners and existing concrete tunnel walls.
At the front working station, divers were able to raise and lower two rings, ratchet up assemblies horizontally, and make intricate rotational and axial adjustments to align to the circumferential bolt patterns of the custom-designed liners. The HPU delivers 3,000 psi at just over 9 gpm and allows divers to run two hydraulic tools simultaneously. The vehicle’s payload capacity exceeds 9,000 lb, enabling transport and placement of two complete rings (roughly 7,500 lb of liner plate) per trip. These two liners allow for a total of 9 ft of installed tunnel liner per trip down the tunnel.
Ballard’s engineering team developed a stainless‑steel liner designed for a 95-ft hydrostatic head and a 50‑year service life, grouted in place. Each ring is made up of three 120° curved plates, which are 54 in. wide and have flanged and bolted longitudinal and circumferential joints for repeatable, inspectable assembly underwater. Integrated jack bolts and dedicated grout ports enabled balanced, sequenced grouting. Bulkhead rings at 50‑ft intervals subdivide grout stages and protect water quality throughout the operation.
BURT’s electric circuits are protected by a line insulation monitor that trips power within milliseconds if isolation is compromised. The lighting system includes three hours of battery backup; twin air bottles mounted on the vehicle provide each diver up to three additional hours of breathable air in an emergency.
Photo courtesy Ballard Marine Construction
After practicing on a mock-up tunnel on land, the team tested BURT on a 324‑ft‑long, 12‑ft‑wide, 15‑ft‑deep wave channel at the university. "We went from a pencil drawing to OSU in 10 months," says Drobny.
The full‑scale mockups and trials informed details such as a symmetrical plate geometry allowing for multiple positions, gasket refinement, and a patented bolt‑by‑bolt sequencing plan that standardizes diver tasks.
Ultimately, "there were days ... where we placed four rings in an 8-hour shift," says Drobny. Between the two tunnels, some 1,300 ft were repaired.
"We want to do more projects like this," says Short. "There are plenty of water mains in the U.S. where it’s a potential solution versus building a new tunnel."
