The tallest building under construction in Canada is underway right now at the southwest corner of Toronto's Yonge and Bloor intersection, still flying under the radar skyline-wise as below-grade work progresses. Under construction since mid-2017, Mizrahi DevelopmentsThe One is bringing a 308 metre 'supertall' tower designed by Foster + Partners and Core Architects to Bloor-Yorkville. Work continues on the building's complicated foundations.

Looking west across Yonge Street to The One, image by Forum contributor Matthew Derohanessian

We last checked in on the 85-storey condo and hotel tower at the end of January, when work had just begun on drilling the "mega caissons" that will support the tower's hybrid exoskeleton support system. After another month of work, 24 of the 32 mega caissons have now been created in the substrate, and the remaining 8 are expected to be completed by mid-March. 

Mega caisson installation at site of The One, image by Forum contributor AdamS

The caissons are being excavated with a Bauer BG 55 (BS 115) drilling rig, boring holes 3.65m in diameter and extending 30 metres into the earth below. Rebar cages weighing 40 metric tonnes each are then lowered into the boreholes with the site's specialized Link-Belt TG2300B crane, and are then filled in with concrete.

Rebar cage for caisson at The One, image by Forum contributor drum118

The massive volume of these boreholes requires large quantities of concrete—378 cubic metres per caisson. Coordinating these large concrete pours is a complex task, and recent photos show long processions of concrete trucks along Yonge Street. For each caisson, 18 truckloads worth of concrete is required. 

Trucks delivering concrete to site of The One, image by Forum contributor androiduk

Down in the pit, a red-painted Amherst concrete pump is being used to feed the liquid concrete into the boreholes, and that work is continuing today, despite the snow.

Concrete being pumped into mega caisson for The One, image by Forum contributor AdamS

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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Related Companies:  Core Architects, Foster + Partners, GFL Environmental Inc., Live Patrol Inc., Mizrahi Developments, RJC Engineers, The Planning Partnership