The Second Narrows Water Supply Tunnel project broke ground in early 2019 and the substantial completion milestone was achieved in January 2025. It replaces three of Metro Vancouver’s critical water mains (the Second Narrows Crossing) that convey drinking water from the North Shore watersheds, across the Burrard Inlet, and into the City of Burnaby, where it is distributed to Metro Vancouver’s municipalities.

The Second Narrows Water Supply Tunnel was the first pressurized-face bored tunnel crossing of the Burrard Inlet, and is particularly challenging as it intersects the full range of ground conditions from gravelly soils at the north to weak rock at the south and was required to be designed for 1:10,000-year return period seismic-induced ground motions, which includes liquefaction at the north shaft and the tunnel. Additionally, the tunnel is subject to groundwater pressures above 6 bar, making this tunnel one of the highest-pressure soft ground tunnels ever built in Canada. These challenges required significant thought and effort during final design and a technically capable contractor team during construction.

Support of excavation (SOE) includes a 60-metre-deep, 16-metre-diameter tunnel boring machine (TBM) launch shaft in North Vancouver; a 5.8-metre-diameter segmentally lined tunnel under Burrard Inlet; and a 110-metre-deep, 10-metre-diameter TBM reception shaft in Burnaby.

The project’s permanent structures include three fully lined and coated steel pipelines installed within the shafts and tunnel; a partially below-grade, large valve chamber at the north site, and a fully buried chamber at the south site; and tie-in pipelines installed in shallow trenches between the valve chambers and Metro Vancouver’s existing water distribution network.

To facilitate the installation of the project’s permanent structures, extensive earthworks and robust support of excavation were required, including two deep shafts, a deep bored tunnel, and shoring systems for valve chambers and shallow tie-in pipes. The project’s stringent design standards, including the 1:10,000-year return period seismic design criteria and its challenging site conditions, dictated that a balance between meeting project objectives and ensuring constructability was required, and as a result, offered a unique opportunity for the engineers and contractors to innovate and develop their expertise in cutting-edge technologies. The TBM launch shaft (North Shaft) initial lining, for example, consists of unreinforced concrete slurry wall panels installed to a depth of 80 m and to rigorous verticality tolerances, pushing the limit of slurry wall technology. The North Shaft final lining was designed as a smaller structure inside the launch shaft, with an annular space between the two—an innovative solution to reduce seismic demands in liquefiable soils, improve constructability, and reduce materials. The tunnel was required to meet standards at the upper limit of a TBM’s capability through mixed-face, soft ground conditions with high external groundwater pressure. To build the tunnel safely and within tolerance, the contractor furnished a state-of-the-art, 6.7 m diameter slurry TBM—the first of its kind in Canada—and utilized experienced specialists to operate it.

The three new large water mains will meet the region’s long-term needs for high-quality drinking water and ensure reliability in the event of a major earthquake. The project faced numerous challenges, including design and construction of highly complex underground structures in challenging ground conditions and construction challenges such as during COVID-19. The project was substantially completed in January 2025. Work to tie into the existing system will be completed within the next few years.