sliplining culvert in Montreal

A Grand Project Beneath Montreal – Sliplining a 154-year-old Brick Culvert with GRP

Having a sewer system that is more than 150 years old means that the underground infrastructure has far outlived its useful life. As a matter of fact, systems of this age — more often than not — are nearing a catastrophic event.

In an effort to prevent these kinds of catastrophic failures, the City of Montreal has proactively looked at its system and routinely repairs and upgrades its infrastructure. Such was the case in 2019 when the Montreal Waste Water Department tendered the rehabilitation of the Grand Trunk connector project. The project called for the rehabilitation of 745 m of egg-shaped brick culvert installed in 1865.

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The City specified that the project be complete using the sliplining trenchless method with glass reinforced plastic (GRP) pipe. The end result was the creation of a structurally-sound pipe with improved hydraulic capacity and extending the life of this sewer well into its 200’s.

The winning bid for the project went to Lafontaine Excavations Inc. headquartered in Lévis, Québec. Predominantly an open-cut contractor, Lafontaine’s trenchless experience is in sliplining and cured-in-place pipe (CIPP) relining using ultraviolet technologies.

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sliplining culvert in Montreal

According to Mathieu Asselin, ing., estimator–project manager, at Lafontaine, this project marked the company’s fifth sliplining project and the first using GRP liners from Channeline International. Lafontaine received a notice to proceed in July 2019 and the bulk of the work on the project was complete in March 2020.

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Completed in two phases, the project took place beneath Rue Grand Trunk in a primarily residential section of the Pointe-Saint-Charles neighborhood in the borough of Le Sud-Ouest. Phase 1 was a 425 m run between Shearer and Wellington streets and Phase 2 was the rehabilitation of 320 m of sewer between Hibernia and Shearer streets. Through the length of the project the egg-shaped brick sewer measured 1,800 mm by 1,200 mm.

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sliplining culvert in Montreal

Lafontaine chose Channeline because its GRP product 100 per cent matched all the City’s specifications and Channeline could deliver the liner the quickest. The new collector has an inside diameter of 1,000 mm by 1,452 mm (OD 1,038 mm by 1,490 mm).

“All of the brick was unstable, and the City needed to do something. In the bid contest, the City of Montreal specified using the sliplining method with GRP. They chose sliplining instead of a flexible liner to increase the stability of the collector and the ground around the collector,” says Asselin. “GRP was a good option for rehabilitation, even though the diameter of the collector was reduced, the flow capacity was increased because of the Manning’s Coefficient — the friction between the wastewater and the GRP — is a lot smaller than the old brick making the flow capacity higher.”

Before beginning the sliplining work, Lafontaine was tasked with completing initial cleaning and preparation work including repairing the cracks in the brick sewer via grouting. It is during this portion of the project that the team discovered two things.

The first was an approximately 10-m long deformation in the 425 m run of the pipe that would be impossible to line through. Lafontaine completed that repair via open-cut construction methods, but other than that portion the entire Grand Trunk rehab project was completed via trenchless.

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The second was the discovery of a concrete portion of the wall inscribed with “À la mémoire des anciens – Honneur à vous,” which translates to “In memory of the elders – Honor to you.” And “Ici sont mort les égoutiers en travaillant comme des chiens,” which translates to, “Here died the workers working like dogs.” The names of those who lost their lives building the sewer were also inscribed on the panels.

grand trunk memorial wall

“The city didn’t know the presence of the panel, so when we found it we took photos for the City,” Asselin said. “We had to slipline over it because we could not remove a panel of that size because it is an integral part of the wall and it would be unsafe to remove it.”

With the preparation work complete, the crew received its first shipment of Channeline in November 2019. Lafontaine completed the first phase in January 2020 with the start of Phase 2 commencing immediately after and concluding in February. A bypass was required for the 320-m section because the longer section was at the head of the collector. According to Asselin, the bypass was mainly to divert flows from a secondary connector that tied into the section being rehabbed.

“The biggest challenge we faced was for our workers. They had to work all day in the collector in the wastewater and each run only had one access point making it difficult work,” says Asselin. “Each section had one access shaft and we installed more than 300 sections of Channeline GRP. The sliplining was fast for sure, but it was the other works that needed to be completed that took time.”

sliplining culvert in Montreal

In addition to grouting the annular space to hold the GRP liners in place, crews had to reinstate more than 120 lateral connections. It was at one of those connections that the project hit its only snag.

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Grouting is done in short sections and the amount of grout is closely monitored. The installation crew noticed it was using more grout than it should, prompting investigation. The crew suspected that a crack in the brick allowed the grout to go out of the sewer, and seeped into a collapsed lateral service with the grout ending up inside of a building. After this discovery, the crew fixed the problem and the work returned to normal.

“The Grand Trunk project was our fifth sliplining project and what we learn [with each project] is that each project is different with its own difficulties and challenge,” Asselin says. “We can’t think a project will be easy and fast because it is the same condition as another project we did before.”

Mike Kezdi is managing editor at Trenchless Technology Canada.