Shotcrete Support for the Seymour Shaft and Shaftbase TBM Launch Chamber Seymour Capilano Twin Tunnels Project, Vancouver, BC

The Seymour Capilano Water Filtration Project includes major underground works comprising twin, 3.8 m diameter, 7.2 km bored tunnels, the 180 m deep Seymour Shaft as the main construction shaft, and the two 275 m deep Capilano raisebore shafts. Construction started in the fall of 2004 with the excavation of the 12 m diameter, 180 m deep, Seymour Shaft by conventional shaft sinking methods through 30 m of dense glacial deposits followed by 150 m of granitic bedrock. An alternative shaft support system consisting of lattice girders, mesh and dry mix shotcrete was implemented by the Tunnel Contractor for sinking through the dense glacial deposits. Shaft support for the bedrock portion followed the base design comprising pattern rock bolts, mesh and dry mix shotcrete. The Tunnel Contractor took advantage of a local batch plant to provide batched shotcrete mix during the day shift and used a manufactured shotcrete product during the night shifts. Following the completion of the main shaft a large shaftbase chamber has been excavated and supported using a similar support system. The dry mix shotcrete was thoroughly evaluated through quality control and quality assurance testing during construction and performed well to meet the project requirements to provide stable and safe shaft and shaftbase excavations to allow for the completion of subsequent underground works.