With the new Champlain Bridge set to open next month, the process to tear down the old bridge will start next year.
Dismantling the 3.4 km span over the St. Lawrence River will cost $400 million and take three years.
The federal bridge corporation says the bridge cannot be blown up or dropped into the river because it is a working waterway. Crews also plan to recycle as much material from the bridge as possible and to redevelop the shoreline.
Tearing it apart will require crane workers based on land, as well as crews manning heavy barges.
“There will be cranes, there will be boats, there will be transport of material by trucks,” explained Anne Belhumeur, senior director of Champlain Bridge Projects.
One critical complication in dismantling the bridge is that it spans the heavily-trafficked St. Lawrence Seaway.
Most of the bridge is made of 50 concrete spans, containing a total of 350 concrete beams that weigh 220 tonnes apiece. Tearing this apart without causing a sudden collapse will have to be done in sections and requires careful planning.
The portions of the bridge that go over the Seaway are made of steel trusses.
Cutting these apart cannot be allowed to interfere with the flow of freight traffic along the Seaway, so planners are hoping to do most of the work on these sections from January to March when ship traffic is lightest.
The steel trusses would need to be attached on either end, cut, and then lowered to barges on the water.
"Getting off the trusses and then the post tension and all that is a challenge, it's an engineering challenge," said Sandra Martel, the interim Chief Executive Officer of the Jacques Cartier and Champlain Bridge Corporation.
"That's why we talk about deconstruction. It's not only to dismantle and it's done. There's a lot of calculation that has be done to ensure the pieces will be holding themselves.
In all the bridge contains 250,000 tonnes of concrete, 25,000 tonnes of steel, and 12,000 tonnes of asphalt.
The first step is to inform the public and to close off both ends of the bridge to traffic, which will happen over the next two months.
The replacement for the Champlain Bridge was supposed to be finished in December, but due to delays, the existing span can only start coming down next year.
“For the deconstruction they're working in parallel so we will start maybe in March 2020,” said Belhumeur.
The inbound lanes of the new structure will open on June 3; the outbound lanes two weeks later.
The hope is to recycle or reuse as many pieces of the old bridge as possible.
The old Champlain Bridge will officially close on June 17. By 2022, the entire structure will be gone.
The Bridge corporation is hosting information sessions in downtown Montreal on May 8 and 9, in Nuns' Island on May 11, and in Brossard on May 13.
- More information here.