For the 20 months since shovels first went into the ground for Mizrahi Developments' highly-anticipated The One, work on the Foster + Partners and Core Architects-designed 'supertall' tower has been progressing relatively out-of-sight several levels below Toronto's Yonge and Bloor intersection. For months now, the focus has been on creating 'legs' below the level of the excavation pit upon which the foundation levels will rest, and support the 308 metre-tall tower's signature hybrid exoskeleton structure. Those are known as 'mega-caissons,' and there are 32 of them. 

The One, Mizrahi Developments, Foster + Partners, Core Architects, TorontoAerial view of The One site at Yonge and Bloor, image by Forum contributor Benito

Drilling into the ground to create them them has involved a Bauer BG 55 (BS 115) rig, boring holes 3.65 metres in diameter and 30 metres deep. Then, tube-shaped rebar cages weighing 40 metric tonnes each were lowered into the holes and then filled with 378 cubic metres of concrete each.

Work on the mega-caissons recently wrapped up, allowing the demobilization of the equipment used to create them. A recent image of the site shows a section of the disassembled Bauer BG 55 rig being hoisted from the pit by the specialized Link-Belt TG2300B crane. 

The One, Mizrahi Developments, Foster + Partners, Core Architects, TorontoBG 55 section being removed from pit at The One, image by Forum contributor Benito

With the caissons in place, preparations for cap foundations is planned to start in the coming days, with delivery of forms and tooling from the formwork subcontractor imminent. Additional excavation equipment will be delivered to the site in the coming days to support detailed excavation on select parts of the pit, expected to begin next week.

Other tasks currently being carried out include the installation of sheet piling for shoring at the firefighters' elevator, as well as dewatering within the secant (perimeter caisson) wall, and drilling of four additional caissons below the site's preserved heritage component. Drilling of these caissons and the removal of supporting equipment is expected to be completed no later than April 20th.

The One, Mizrahi Developments, Foster + Partners, Core Architects, TorontoThe One, image courtesy of Mizrahi Developments

Meanwhile, as all of this work takes place below ground, the City of Toronto is now processing a building permit application received on April 3 that will allow work on The One to proceed up from the foundations.

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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