As we near the end of work that will connect Montreal Airport to the Metropolitan Express Network (REM), we were able to descend into the heart of the newly dug tunnel.
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The descent to the site is through a trench about 600 meters long located 15 meters from the surface. All around, CDPQ Infra, which is responsible for the project, has set up the necessary infrastructure to produce the concrete, treat the water, transport the materials and remove the excavated material.
The tunnel itself, 2.5 kilometers long, is 35 meters below the surface.
The concrete walls were excavated and installed using a tunnel boring machine. According to CDPQ Infra, this is the first time in Quebec that a tunnel boring machine that can perform both of these tasks has been used.
“In our case we had two situations. We had both loose soil and rocks. That’s why we used this technology,” explained Marc-André Lefebvre, our tour guide and communications director at NouvLR.
The tunnel boring machine has a diameter of around 7.5 meters and a head made of 47 discs, each breaking up the ground with a pressure of 25 tons. The clippings are then evacuated to the surface by an endless auger on a conveyor belt.
In the front area, a control cabin ensures that the tunnel boring machine works properly. “It’s a job that requires a lot of experience. For a project like this we need to make sure we are looking for the best in the world to ensure we have the expertise required. This made it possible to import this knowledge to Quebec to train people,” explained Mr. Lefebvre.
The “shield”, representing the front part of the aircraft, is 30 meters long and weighs 430 tons. With each 1.5 meter advance, the rams retract to place segments that will support the tunnel.
Each ring consists of seven voussoirs that complete the circle. A total of 1045 rings will be installed over the 2.5 kilometers of the tunnel.
Concrete is then poured into the space between the rock and the ring to ensure a complete seal. This is one of the points where “a lot still needs to be done”.
During the excavation, around 100 workers worked in three shifts of 12 hours each.
“In the middle of winter there are people who come here in the dark, who come out in the dark and who spend their day in the tunnel without ever seeing the light of day. It is extremely difficult work,” said Mr Lefebvre.
As we advanced, the ground was covered with water. A normal situation, according to the explanations given to us, since the rainwater drains through the ditch towards the tunnel. Upon completion of the work, the area should be completely sealed.
Finally, a raft, a stable platform, is installed slightly off the ground to place the REM rails on. The various electrical cables required for proper functioning are hidden underneath.
Over the next few months, the teams will dismantle the tunnel boring machine that was only used for this tunnel.
Aéroports de Montréal (ADM) will be responsible for building the station leading to the tunnel. No date has yet been given for the inauguration of the future station, although the REM is scheduled to be inaugurated in 2024.