REPORT | NORTH AMERICA
In Toronto, a US$32.1bn subway expansion, said to be
the largest transit expansion in Canadian history, is under way. In June, a ground-breaking ceremony was held for the 7.8km Scarborough Subway Extension. Strabag has been awarded the contract, which also includes supplying the TBM. Meanwhile, West Connectors has been awarded the contract for the 9.2km Eglinton Crosstown West Extension, which includes 6km of tunnelling. Boring on this project is due to start in spring/summer 2022. Trans Mountain Corporation, which operates
Canada’s only pipeline system transporting oil products to the West Coast, is boosting capacity with the Trans Mountain Expansion Project. The scheme includes a 2.6km tunnel to house three 30in (762mm) delivery pipelines, connecting the Burnaby and Westbridge Marine terminals.
Excavation of the 4.43m-diameter tunnel began in
May and is expected to proceed at 15m per day. The Herrenknecht dual-mode TBM can be changed from EPB shield mode to an open-mode configuration. This will accommodate the wide variety of geotechnical features, and the sudden change in geotechnical conditions. Nearby, a new eight-lane immersed-tube tunnel
is planned to replace the George Massey Tunnel on Highway 99, south of Vancouver. The US$3.25bn project is scheduled to open in 2030. And there is also Elon Musk’s penchant for ‘Boring
Loops’. The latest are Florida’s Las Olas Loop, a 4km, bi- directional tunnel which will carry passengers in Teslas from downtown Fort Lauderdale to the beach; and the Ontario Airport Loop, for which The Boring Company has also suggested a bi-directional system.
SECOND NARROWS WATER SUPPLY
TUNNEL, VANCOUVER Currently under construction by Traylor-Aecon, with McMillen Jacobs as engineer of record for all underground structures and prime consultant for the design team (which includes AECOM and Golder), the US$355m project aims to make the region’s drinking water system more resilient to earthquakes. It will also meet growing demand, conveying high-quality drinking water from Vancouver’s North Shore to households in the region. Designed to meet current seismic standards, the tunnel will replace three shallow, buried water mains built in 1948, 1954 and 1978 which are vulnerable to earthquake damage and nearing the end of their service life. Excavation was undertaken by a 6.64m-diameter Herrenknecht TBM (Lynn-Marie) – the first mixshield/slurry TBM to be used in Canada. The machine, which was chosen for the anticipated pressures
Mining at up to 30m below the inlet bed, the TBM had to be able to
provide around 6.5bar of support pressure. Along the alignment it encountered three distinct geological zones: ● Sand and silt mixtures. ● A soil-to-rock transition zone with cobbles and boulders, and ● Mostly weak sandstone. According to MacMillen Jacobs: “The bentonite slurry provided
excavation support at a pressure controlled by mechanical means via a compressed air bubble. The slurry circuit is a closed system,
and geology, was launched in autumn 2020 from a 60m-deep, 16m-diameter shaft on the North Vancouver side of Burrard Inlet. MacMillen Jacobs state that for support of excavation, the launch shaft includes 22-80m-deep unreinforced concrete slurry panels installed by hydromill in a challenging area of sandy soils with a high cobble content and high hydraulic conductivity. “The TBM was launched from a pressurised ‘launch lock’ with no ground improvement outside the shaft. Therefore, the launch lock was required to seal against the full-face support pressure (around 6.5bar) prior to breaking through the shaft wall and to provide support for TBM thrust and rolling action.”
and bentonite slurry is constantly cycled in and out of the excavation chamber while mining. Bentonite acts as a transport medium for excavation cuttings, which are piped out of the tunnel, separated at a treatment plant, and recycled back into the system.” The 5.8m ID segmentally-lined tunnel terminates in Burnaby on the south of the inlet in a 110m-deep, 10m-diameter reception shaft excavated through rock using conventional techniques. It was lined with synthetic fibre-reinforced shotcrete and steel ribs. By the time construction is completed, anticipated for 2025, three
steel water mains (1.5m- and 2 x 2.4m-diameter) will have been installed in the tunnel.
26 | November 2021
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