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The Second Narrows Water Supply Tunnel will replace three existing water mains installed between 1948 and 1978. The 1.1-kilometer tunnel crosses beneath the Burrard Inlet from North Vancouver to the City of Burnaby. The new water mains are nearly 100 feet below the inlet and carry twice as much water while ensuring seismic resiliency.
Two tunnel shafts were constructed for the project. The northern shaft, located in North Vancouver, is 200 feet deep and 52 feet in diameter. Tremie concrete was placed in the shaft allowing for dewatering and the bottom 50 feet of shaft lining concrete to be installed. The southern shaft, situated in Second Narrows Park, is 360 feet deep.
The tunneling process presented unique challenges which included a short mode launch of the Herrenknecht slurry tunnel boring machine (TBM), tunneling through soft ground conditions, and facing high pressures of up to 6.5 bar. Ballard Marine Construction was on standby to perform cutterhead interventions via saturation diving. Traylor previously had only two projects experience similar face pressures with slurry machines— the University Link U220 in 2012 and the South Bay Ocean Outfall in 1997.
After the construction of the tunnel and two shafts were completed, the valve chambers at each tunnel end were built. The chambers connect 1,000 feet of buried pipe to the three pipelines inside the tunnel. Subcontractors finished electrical, instrumentation, and HVAC systems in time for final testing with the client. Hydrostatic testing was successfully conducted on two 8-foot diameter pipes and one 15-foot diameter pipe to a test pressure of 404 psi.
The Traylor-Aecon General Partnership’s Second Narrows Water Supply Tunnel project was the 2024 recipient of TAC’s Canadian Project of the Year (under $300M CAD) Award. This honor recognized the team’s demonstration of exceptional engineering skill and understanding of underground construction for a project in Canada.
