The Second Narrows Water Supply Tunnel project will replace three existing water mains that were installed in 1948, 1954, and 1978. The 1.1-kilometer tunnel will cross under the Burrard inlet from north Vancouver to the City of Burnaby. The new water mains will be nearly 100 feet below the inlet and carry twice as much water as the existing mains that are seismically vulnerable and operating near full capacity.
Two tunnel shafts will be constructed. One is approximately 200 feet deep, located in Metro Vancouver’s yard in North Vancouver, immediately north of the inlet and east of the Seymour River. The other 360-foot-deep shaft is situated in a forested area of Second Narrows Park on the south side of the inlet in Burnaby.
The north shaft 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 the shaft lining concrete to be placed. The new Herrenknecht slurry tunnel boring machine (TBM) was assembled simultaneously on the surface. Due to the small diameter of the shaft, the TBM was launched incrementally, initially with the shield in the shaft and trailing gear on the surface. As tunneling progressed, the trailing gear for the TBM was lowered into the shaft in two stages.
After successfully launching the mix shield TBM in September 2020, the entire TBM is now underground and heading toward the other side of the Burrard Inlet. Ballard Marine Construction is on standby to perform hyperbaric interventions via saturation diving. The only other Traylor projects to reach that face pressure were University Link U220 in 2012 and the South Bay Ocean Outfall in 1997.
The south shaft reached its full depth of 360 feet in late May 2021, having utilized additional pre-excavation grouting to mitigate higher than anticipated groundwater inflow. At this point, the project’s focus turned to installing three new water mains inside the finished tunnel. The new mains will be connected to the existing system in new valve chambers and restoration will take place at Second Narrows Park between fall of 2023 and spring of 2024.