HMM also incorporated the relatively new use of guide rods in the circle joints of the lining segments, adds Tattersall. "These are hard plastic dowels that are set into the radial joints to guide the alignment of the segment as it is slid into position so that the contractor cannot do a bad build. To fit them together, you have to have them in the right orientation, not just get close enough and sledgehammer them in," he says.
The TTC consented to the fabrication of 100 tunnel rings that use steel-fiber reinforcing instead of the traditional reinforcing steel cages, adds Tattersall. "Steel fibers are sort of the way the industry's going. The TTC was a little cautious about it but agreed to do 100 rings and monitor to see how they perform," he says. HMM had used steel fibers in tunnel linings for the Crossrail project in London, Tattersall notes. "There's no significant track record yet on the durability over a long period of time, especially considering the corrosion due to deicing salts. But it reduces the costs significantly. You don't have to fabricate and fit cages to a high tolerance. You just put the fiber into the concrete mix and pour them into the mold," he says.
Tunneling through glacial till and silty, sandy and clay-like layers, Holey and Moley completed 1.4 km between the Sheppard West and Finch West station sites last year and 1.2 km between the Sheppard West and existing Downsview stations at the southernmost point this spring. Torkie and Yorkie dug 1.7 km from Black Creek Pioneer Village (formerly Steeles West) southward to Finch West in 2012. Then, they relocated to the Highway 407 station site for the 945 m of tunneling that completed in June.
Station Styles
Designs of the six stations were divided equally among three teams. AECOM, Arup and the Spadina Group Associates—a joint venture of Stevens Group Architects, Lea Engineering, Halsall Associates, and SMC Alsop Architects—each led design of two stations. AECOM teamed with the architecture firm Aedas on Sheppard West and Highway 407. Starting in 2008, "we pretty much were trailblazers for establishing the design standards and encountering regulatory issues," says Abbas Khayyam, AECOM's deputy project director. He notes that while the TTC selected an international array of designers, it also employed a standard manual. "That dictated the structural designs, and we had to justify it when we deviated from them."
One of the major challenges in station construction involved the high water table, which threatened to "float" upward the structural boxes. "It was a balancing act of thick walls and light stations," says Khayyam. At the three-level Sheppard West station, which includes an intermodal connection to the Go Transit regional system, contractor Aecon Group Inc. is using 70 micropiles about 150 mm in dia and driven approximately 11 m deep to anchor down the station box, says Mary Van De Gevel, AECOM project manager.
The work also included a 30-m-long, 15-m-wide, 20-m-deep tunneling extraction shaft in the middle of a street while protecting a 600-m-dia high-pressure gas main and maintaining traffic on either side, says Marty Harris, vice president of estimating and construction with Aecon, which holds the $279-million contract. Crews also temporarily relocated a freight rail line that runs through the site.
At the Finch Station site, designed by the Spadina Group team, OHL-FCC performed sequential excavation about 25 m deep beneath a hydropower field and major oil, gas and water lines, says Zander. Bondfield Construction has the $126-million station contract. North of Finch, York University station is squeezed at an angle between two campus buildings, with the curving aluminum-clad roof "wings," conceived by architect Foster + Partners, rising just above grade. "We had to shorten the station to the absolute minimum to fit it in," says Keith Greville, Arup project manager.
EllisDon Civil Ltd. recently began mobilizing its $118-million contract, which came after OHL-FCC installed pilings and relocated a utility tunnel so it could run above the subway station. OHL-FCC is also building the Highway 407 station, cast as a monolithic structure to resist buoyancy and eliminate construction joints, says AECOM's Khayyam. OHL-FCC came up with a plan to use conveyor belts to transport tunneling muck out of the site, says Zander.
Allowing for ambitious transit-oriented development is key at the Black Creek Pioneer Station, where Walsh Construction Co.'s Canada group holds a $165-million contract to build a distinctive building of Corten steel with a coppery facade. The Spadina Group had to redesign the site four times in order to accommodate development-block plans and potential future light rail, says Kervin.
