Excitement is building as a pit is beginning to take shape at Yonge and Bloor in Downtown Toronto, the site of where Canada's tallest building will soon rise: Mizrahi DevelopmentsThe One. The complexity of the 85-storey project, designed by Foster + Partners with Core Architects, has led to various site-specific technical and engineering challenges, and today we'll take a closer look at the construction methods at play for this "supertall" landmark.

Aerial view of The One site, image by Forum contributor Benito

The recent assembly of ground-level formwork atop an active excavation pit seemed at first that it might be a sign of top-down construction, a method of construction that uses lateral bracing to allow underground levels to be formed from grade downward. This method, not yet seen in Toronto, had been considered for this development, but after checking in with representatives at Mizrahi, we can confirm that the conventional shoring and excavation method has been settled on for its simplicity and scheduling. 

Aerial view of The One site, image by Forum contributor Benito

What we are actually seeing being formed is a temporary slab that will be used to stage materials and equipment, supporting the excavation and construction below, while not taking up space on Yonge or Bloor streets, reducing the impact on traffic and costly lane closures at the busy intersection.

More steel rebar is placed in advance of the concrete pour for the temporary slab, image by Forum contributor Benito

With the top-down method out of the picture, we will see a standard excavation process follow over the coming months, which will include the installation of tiebacks and braces as the pit get deeper. Excavation is expected to reach foundation depth by September. If this target is met, we should see concrete forming rise above grade late in the first quarter of 2019.

Tieback drilling at The One site, image by Forum contributor Benito

Like many Foster + Partners designs, The One's structural system plays an integral role in the building's look. The hybrid structural exoskeleton at The One has been an advertised since the earliest renderings were revealed in 2015, and we can now confirm that this system will be constructed with a composite RSC (Reinforced Steel Concrete), essentially steel encased in concrete. This differs from the steel diagrid structures seen on Foster's The Gherkin in London and The Bow in Calgary, bearing more similarities to the system employed at the new CITIC Bank Headquarters in China.

Hybrid exoskeleton at The One, image courtesy of Mizrahi

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 threads, or leave a comment in the field provided at the bottom of this page.

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