Construction for Mizrahi Developments' The One is heating up at the southwest corner of Yonge and Bloor in the heart of Toronto. The early stages of work for the 306-metre 'supertall' tower designed by Foster + Partners and Core Architects crossed a milestone midway through November with the installation of a specialized high-capacity tower crane, and the latest photos of the site are revealing even more specialized equipment arriving, this time for drilling caissons for the tower's hybrid exoskeleton.

Overview of The One site, image by Forum contributor AdamS

The site's perimeter caisson shoring wall allowed excavation of the building's footprint, and now, eight "mega caissons" will be drilled into the bottom of the excavated pit. At 3.65m in diameter and extending 30m below the pit, these massive caissons will form the footings for The One's exoskeleton, which will transfer the tower's loads across the building exterior and down into the bedrock.

Large rebar cage at The One, image by Edward Skira

A Bauer BG 55 (BS 115) rig is now in place at the base of the pit. This rig will use its enormous drill bit to bore out the large caissons. Once drilled, large rebar cages—each weighing 40 metric tonnes—will be lowered into the boreholes and filled with 378 cubic metres of concrete. The weight of the drilling equipment and rebar cages is one of the reasons that the ultra-high capacity crane, covered in the previous story, was necessary.

Drilling equipment at the base of The One's excavated pit, image by Forum contributor skycandy

The behemoth drilling rig—supplied by ECA Canada and sporting Anchor Shoring livery—was used earlier in The One's construction, working alongside a pair of other rigs during the initial shoring phase just over one year ago. With much larger drill attachments, the bright green-painted BG 55 is now primed to begin the complex operation.

Large rebar cage at The One, image by Edward Skira

Additional information and images can be found in our database file for the project, linked below. Want to get involved in the discussion? Check out the associated Forum thread, or leave a comment in the field provided at the bottom of this page.

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