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Mill Creek Tunnel Reline

Edmonton, AB,

Reline

Owner:

EPCOR

Engineer:

EPCOR

Contractor:

Whitson Contracting

Installation:

March 2020

Technical Description:

  • Product: DuroMaxx® SRPE
  • Diameter: 30-inch
  • Length: 80' LF (5' - 6' sections)

In early 2020 Contech and Armtec responded to a pricing and delivery lead time request from Whitson Contracting, who was performing emergency work for EPCOR in Edmonton, AB. An existing sanitary sewer tunnel required rehabilitation. Over the years, the concrete tunnel had experiences corrosion and wear to the point where the steel reinforcing cage was showing, and in some cases, missing.  The determination was made by EPCOR that the repair had to be completed immediately to address catastrophic failure concerns.

While many options were considered, reline was the most expedient repair approach, and Whitson began looking for materials which would fit into the existing tunnel geometry. The tunnel’s oblong shape created challenges. While there are non-circular reline material options available, none of them were immediately available for this project. In some cases, months of material lead time were required. Instead, Whitson looked at using two circular pipes, one on top of the other. The bottom pipe would consist of 30” steel reinforced polyethylene pipe, or DuroMaxx, while the top pipe would be a smaller diameter solid wall PVC material. Grout would be used between the new liner pipes and the existing tunnel. The grout serves three purposes: (1) to transfer loads between the old tunnel and new liner pipes; (2) hold the new liner pipes in place; and (3) separate the two new pipes from each other.

After a plan was created for the repair, jobsite constraints had to then be taken into account. First and foremost was access to the affected tunnel. Reline uses segments of pipe, which are slid into the existing tunnel. Generally speaking, access would be through the sanitary sewer system outlet or through a bespoke shaft. This jobsite would require a shaft, and the site limited the length of the shaft to 6’. Most pipe is manufactured in standard lengths of 12’, 14’, 20’, or even greater, thus creating another challenge. Contech was able to manufacture the 30” DuroMaxx in 5’-6” piece lengths to fit through the shaft and into the tunnel.   

The DuroMaxx was slid into the 80’ long oblong tunnel lace piece by piece, creating a train of pipes which were joined by a polyethylene covered, steel reinforced bells and spigots. The superior joint would help keep the grout on the inside of the pipe from entering the inside of the pipe. Once the entire length of DuroMaxx was in place, grouting would need to be completed to move on to the smaller diameter portion of the project.

Contech and Whitson worked closely to determine the buoyant forces acting on the pipe during the grouting phase. Whitson determined that the best way to counteract the buoyant forces was to use plant-installed grout porting at the crown of the pipe. During the grouting phase, the grout ports would be opened and supports be slid through them and braced against the crown of the existing tunnel. In place, the supports held the DuroMaxx in place until the grout reached initial set.

The project was installed well, and the tunnel was repaired in a very quick time frame. 

Technical Description:

  • Product: DuroMaxx® SRPE
  • Diameter: 30-inch
  • Length: 80' LF (5' - 6' sections)

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