Second Narrows Tunnel

Diaphragm Wall Expertise in Metro Vancouver’s Second Narrows Tunnel

Metro Vancouver is advancing the Second Narrows Tunnel, a critical water supply project under Burrard Inlet, contracted to Malcolm Drilling for the installation of a diaphragm wall ring.  This project is one of five new regional water supply tunnels designed to meet current seismic standards, ensuring reliable drinking water delivery in the event of a major earthquake.

The tunnel, 3,609 ft. long with a diameter of 22 ft., is excavated deep underground using a tunnel boring machine. It will increase the existing system’s capacity to meet the growing population’s long-term needs. The 50 ft. diameter entry shaft (North Shaft) is 275 ft. deep, constructed through challenging alluvial deposits with a high percentage of cobbles and boulders, and groundwater level at ground level. The support of excavation (SOE) design, based on a 48 in. wide un-reinforced diaphragm wall ring, addresses tight verticality tolerances of only 0.4%. State-of-the-art hydro cutter equipment, along with real-time verticality monitoring systems, was employed to meet these requirements. Malcolm Drilling overcame challenges posed by subsurface conditions by adopting means and methods to stabilize loose geotechnical formations quickly.

Malcolm Drilling