Second Narrows Water Supply Tunnel
Summary
The Second Narrows Water Supply Tunnel is designed for a 100-year design life and to withstand and remain operational following a major earthquake. This 1.1‑kilometer (0.7 mi) tunnel project consists of three new water mains within a precast segmentally lined bored tunnel with a 5.5 meter (18 ft) inside diameter and the ability to withstand up to 6.5 bar of pressure. The new crossing also provides increased capacity to meet future demand and be safe from scour impact.
- 1.1-kilometer (0.7 mi) water supply tunnel
- Two deep shafts
Scope of Work
The tunnel was excavated with a slurry tunnel boring machine (TBM) through granular soil, mixed face conditions, and sedimentary rock under Burrard Inlet. The steel water mains range in diameter from 1.5 to 2.4 meters (5 to 8 ft).
Two deep shafts, located in the District of North Vancouver and the City of Burnaby, respectively, connect the tunnel to the surface.
Challenges & Innovations
Support of excavation (SOE) includes a 60-meter-deep (197 ft), 16-meter-diameter (52 ft) TBM launch shaft in North Vancouver; a 5.8-meter-diameter (19 ft) segmentally lined tunnel under Burrard Inlet; and a 110-meter-deep (361 ft), 10-meter-diameter (33 ft) TBM reception shaft in Burnaby.
Permanent works include three welded steel pipes installed in tunnel and shafts, a reinforced concrete liner in the North Shaft, and a valve chamber on either side of the crossing.