Bridge over icy waters
October 1, 2012 by Andrew Snook
The Deh Cho Bridge is scheduled to open this November in Fort Providence, N.W.T. on Northwest Territorries Highway 3. The two-lane, 1.045-km cablestay bridge will offer residents their first year-round access across the Mackenzie River. It replaces the Merv Hardle ferry, used to transport people and goods over the summer months, and the Mackenzie River Ice Crossing, used over the winter months whenever possible.
Although the bridge is expected to get only 400 vehicles a day, it will be a vital link for residents in the area, as well as companies moving goods or operating mines in the area, where approximately 11,000 fuel loads are transported every season.
Toronto-based Associated Engineering currently manages the project and Ruskin Construction of Prince George, B.C. is the prime contractor.
Contractors and engineers working on the $202-million project have encountered their share of challenges since major construction began in the spring of 2008—the bridge’s icy and remote location; lack of sunlight; and a few other unexpected events.
Fort Providence’s outlying location and small airport, which only handles light planes, created some start-up challenges for the contractor. Since the project is not located near a particular logistics railhead or airhead, the contractor had to set up camp in an isolated area, fly or drive in all logistics support and set up communications via satellite to get the infrastructure ready for the construction site, according to Kevin McLeod, director of highways and marine services for the N.W.T. Department of Transportation.
Coordinating transportation of the bridge’s components required serious strategic planning. The components were built throughout Canada, the U.S. and Europe, including the steel substructure being fabricated in New Brunswick;
the steel truss in Quebec; the deck panels in B.C.; the expansion joints in Switzerland and the staycables in England.
Associated Engineering’s Leslie Mihalik, project manager for northern infrastructure, says various quality procedures were put in place to help prevent delays, including the assembling of the truss in Quebec in a trial fit.
“Given all the challenges with the site—the short summer period and how difficult things would be—we considered it important to assemble the structure elsewhere first, to make sure that everything fits.”
McLeod says the project could be delayed for up to 10 days if the contractor was missing a part or a piece of equipment, which leaves little room for error given the short construction season. The work was on going throughout the winters, but the summer months needed to be capitalized on for the increased daylight and warmer working conditions. The weather starts to get cold in October, doesn’t warm up until May and workers only have approximately five hours of daylight to work in throughout the winter months.
“We’re coping with a severe weather environment in a logistically challenging part of the world,” explains Ruskin president Jim Basha.
Combating the cold
Ruskin has had a crew of 60 skilled tradespeople working on site since 2008; and even the best workers are slowed down by the area’s harsh winter weather.
In addition to being supplied with top-notch winter gear, such as special goggles and face masks, various safety precautions are in place throughout the job site to protect the workers from over exposure and exhaustion, including: 10-minute breaks in warming sheds every hour once the weather hits -30C; temperature and wind monitoring; and upgraded meal plans. McLeod says the extreme cold can affect efficiencies on the job site by as much as 40 per cent.
The equipment also needs to be well prepared for the cold.
“Nowadays, Canadian machines have arctic packages, synthetic oils, heating blankets for sensitive machinery,” McLeod says. “[Ruskin] had folks dedicated to keeping machines warm and fuelled. Even at -45C, it doesn’t take long for a piece of equipment to start freezing. An awful lot of attention and care was taken to make sure the machines were well taken care of… the most important aspect is to be prepared and respect the cold.”
The cranes had some modifications done to them to deal with the impact of high winds; and equipment that relied on hydraulic systems weren’t used below certain temperatures as a safety precaution.
Although the bridge is technically a cablestay, Mihalik says it can be classified as a hybrid.
“It’s a cable-supported truss essentially, which makes it unique,” he explains. “It’s an uncommon type of structure.”
Mihalik says new truss structures are uncommon nowadays since they are very labour intensive.
When the original design, build, finance team was removed from the project (see “Change in management”), a large number of
consultants and an engineering firm were brought on site to perform assessments of the bridge.
“One of the biggest challenges was just to facilitate all the communication and to make it all work in unison,” says Mihalik. “Like a lot of small gears working in a big machine.”
In the end, there was some remedial work that needed to be done, including readjusting the piers.
“They didn’t match the bases properly and so we basically had to have a retrofit design done; and the piers had to be jacked up and strengthened in order to get up to an acceptable level,” says Mihalik.
The bridge was launched from both sides, and given the size of the structure, performing the connection between the two sides was no easy task.
The width of the structure also created a few issues related to the installation of the cables and the bridge’s 278 deck panels.
The concrete deck had not yet been installed, so the contractor had to install a narrow, temporary timber deck on to the structure. This created some challenges for the crews putting the cables in place.
“They had to walk the cranes out to do the work,” explains Mihalik. “They sort of leapfrogged across to the towers to get the cranes there and then install trays to run the cables down, in order to lay them out and lift them up.”
The cables, 12 per tower, had to be laid out on the timber deck in front of the crane. They have a protective coating that could not be rubbed against any other component.
“You can imagine how much the crane movement would be restricted once some of the cables have been installed,” says Mihalik. “It made for some delicate cranework.”
One unique challenge crews and designers had to overcome were the temperature ranges occurring during construction, which had to be accommodated into the design within the expansion joints. Mihalik says sunlight would shine on one part of the bridge for most of the day, creating a large temperature range inside the structure that causes some movement during construction.
“The expansion joint acts almost like an accordion,” explains Mihalik. “The series of parallel beams are connected with rubber glands between them. As the bridge expands/contracts, and the abutments stay in the same location, the beams move closer/further to each other.”
Despite extreme temperatures, short days and new ownership, paving of the bridge began in September and is expected to be complete in early October. Come November, motorists will be able to enjoy a scenic drive over the icy waters of the MackenzieRiver.
***Change in management***
The Government of the Northwest Territories (GWNT) assumed management of the project and its debt in March 2010, after lenders issued a notice of default against the
Deh Cho Bridge Corporation that had signed a contract with the GWNT’s Ministry of Transportation in September 2007, to design, construct, finance and operate the bridge. The original lead contractor, Atcon Construction, was removed from its management and coordination of on-site work in the summer of 2009, due to failure to remedy several notices of default. Ruskin Construction Ltd., the primary sub-contractor responsible for the bridge’s construction to that date, signed a contract to take over as the lead contractor in March 2010. Associated Engineering is currently managing the project with Infinity Engineering Group as the project’s design engineer.