Contractor, Traylor, with consultants McMillen Jacobs, AECON, and Mott MacDonald, have completed tunnel excavation at the 1.1km long Second Narrows Water Supply Tunnel, an important infrastructure project that will make the region’s drinking water system more earthquake resilient and help meet growing demand for safe, high-quality drinking water.
“The tunnel underneath the Burrard Inlet was excavated with the first slurry tunnel boring machine to be used in Canada, and the work was being done up to 100m underground,” said Sav Dhaliwal, Chair of Metro Vancouver’s Board of Directors, the project Client. “Completing this tunnel is an important milestone in this project and a remarkable testament to the innovation that is being used in Metro Vancouver to bring clean drinking water from the North Shore to the rest of the region.”
In order to complete the tunnel, first, a 50m deep vertical entry shaft was excavated on the north side of the inlet, followed by a vertical exit shaft more than 100m deep on the south side. The Herrenknecht slurry TBM — 135m long, with a 6.69m cutting diameter and nicknamed Lynn Marie — launched from the north shaft in August 2020.
The new 6.3m diameter, 1.1km long tunnel was excavated 30m below the bottom of Burrard Inlet, east of the Ironworkers Memorial Bridge. With an internal diameter of 5.8m, the Second Narrows Water Supply Tunnel is one of the largest tunnels ever built by Metro Vancouver. It runs between a Metro Vancouver works yard in the District of North Vancouver and Second Narrows Park (also known as Montrose Park) in Burnaby.
The tunnel drive consists of three reaches: Reach 1, at about 525m is mostly sand and silt mixtures; Reach 2 is a 145m transition zone from soil to rock; Reach 3 is a 415m drive through mostly weak sandstone. In July 2021, the TBM mined steadily through the Reach 2 transition zone, into the Reach 3 sandstone, and stopped for an intervention. Little wear on the cutterhead structure and tools was observed through the first 690m of tunnelling, but most of the discs were replaced for the remainder of the drive.
Now that the tunnel is complete, three steel water mains — one 1.5m in diameter and two 2.4m — will be installed inside and connected to the existing water system with new valve chambers.
“The new tunnel and water mains will replace three existing shallow buried water mains that went into service between the 1940s and 1970s, which are vulnerable to damage during an earthquake and are nearing the end of their service lives,” said Malcolm Brodie, Chair of Metro Vancouver’s Water Committee. “Metro Vancouver is constantly upgrading its water supply system to maintain the quality and reliability of the region’s excellent drinking water, and to make the system more resilient.”
Metro Vancouver supplies nearly 2.7 million people with clean, safe, high-quality drinking water each day. This project is one of five new regional water supply tunnel projects that are being constructed to meet current seismic standards and increase capacity. The Port Mann Water Supply Tunnel went into service in 2017, and preparation is underway for construction of the Annacis Water Supply Tunnel.
Construction on the Second Narrows Water Supply Tunnel began in 2019 and the project is expected to be complete in 2025. The construction budget is $445M.