AN EXACT SCIENCE
Workers use tarps to cover fresh concrete from the rain on one of the cofferdams created to construct footings for the new Champlain Bridge on Thursday. After the dams are installed, the water is pumped out and footings poured into place on the dry riverb
To say building the new Champlain Bridge is a game of inches would be oversimplifying the work: it’s actually a game of millimetres.
Workers have to be so precise that some parts have to be placed within three millimetres of the new bridge’s blueprints.
The $4.24-billion bridge is being built on a tight time frame to meet the Dec. 1, 2018, deadline. To accelerate the process, the Signature on the Saint Lawrence, the consortium building the bridge as part of a public-private partnership, elected to have most of the pieces prefabricated in factories all around North America and Europe, and then assembled on the site.
The bridge’s pillars are made up of 356 concrete blocks, all with a slightly different shape, that fit together like Lego pieces. On Thursday, the media got a tour of the work site for the new bridge just after the first two blocks making up the bridge’s central pillars were installed. The pieces were placed on concrete footings, the foundations of the pillars.
“This segment had to be moved by two millimetres, which we did a few hours ago,” said Frédéric Guitard, the manager of the cablestayed portion of the bridge, showing off the work. “We have surveyors with a computer program checking our on-site measurement with the theoretical measurement.
“Mistakes will accumulate, so if we are not precise, after 22 segments, we can be off by a few centimetres, which is unacceptable.”
He said the segments are placed on elevated jacks until surveyors are satisfied they are in the right place. After that, the jacks are removed and the pieces are fastened onto the footing with concrete. All the other pieces will be glued to each other with epoxy, and then steel cables inside the blocks will be tightened, or post-tensioned, to make the structure more solid.
Guitard said it took about three hours to install each of the first two pieces, and crews expect the process to get faster as they gain more experience.
“It’s going to be mad,” Guitard said. “People driving by will see lots of change in the next few weeks.”
The timetable calls for the bridge’s central pillar to be completed up to the level of the current Champlain Bridge within a month. The crossbeam, which will hold up the bridge’s deck, will be lifted onto the pillar by the first week of October.
Putting together the concrete blocks is the easy part of the job, explained Daniel Genest, director of co-ordination for Signature on the Saint Lawrence.
“The hardest part of the project is just getting out of the water,” Genest said.
The bridge is made up of 74 footings, massive concrete blocks that hold up the pillars. On the Nuns’ Island side of the bridge, the footings are made out of concrete at a work site that juts into the river. The 12 metre by 12 metre blocks, which weigh about 650 tonnes each, are lowered into the water by cranes atop barges, and are guided into place with GPS trackers. They must be placed within 10 to 25 millimetres of the planned schematics. The process takes two to three days from the time the footing is lifted off the ground to the time it is placed in the foundation dug out four metres below the riverbed.
On the South Shore side, the footings are poured in place on site, rather than being pre-fabricated. Workers build massive metal boxes known as cofferdams to dry out the riverbed. Water is pumped out of those dams while the cement is poured.
The work is done overnight, and dozens of concrete mixer trucks line up to pour out 250 cubic metres of concrete — a process that takes between six and seven hours. The blocks are then warmed for 20 days so there is a uniform temperature in the concrete for 20 days after it is poured.
Genest said he expects the underwater work to be completed by the winter. After that, people driving on the old Champlain Bridge will start to see dramatic progress as the new bridge’s pillars will be jutting out of the water by next year. Genest has said repeatedly that respecting the deadline imposed by the federal government is one of the greatest challenges of the project. The consortium faces fines of $100,000 for every day the bridge is delayed.
So far, the project is on time, Genest said, but there have been challenges — namely, new weight limits of 65 metric tonnes for vehicles established by Transport Quebec and weight restrictions imposed on the old Champlain Bridge by the federal corporation managing the deteriorating structure.
“Our transportation plan has had to be adapted,” Genest said, adding that some of the pieces weigh as much as 80 tonnes.
Because of that reality, although the consortium had planned to move all the pieces in by road, it now takes in one-third by truck, one third by rail and one third by boat, adding significantly to the project’s cost, Genest said.
According to the public-private partnership agreement with the federal government, it is the private company that assumes cost overruns. However, in this case because it was an unforeseen expense, the consortium is in discussions with the federal government about the increased transportation costs, said Stéphanie Lassonde a spokesperson for Signature on the Saint Lawrence.