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.
