DFI Magazine January/February 2020 - 87
Shoring and
Foundations
at The One -
Canada's First
Supertall
Building
FEATURE
Currently under construction by Mizrahi
Developments, The One will be Canada's
first supertall building standing at 85 storeys
and 1,005 ft (306 m) in height. The shoring
and foundations for the project were complex and challenging due to the site geometry, urban environment and geotechnical
conditions. The required design capacity of
the foundations for the supertall building
and the proximity of these foundations to
the excavation shoring wall led to many
innovative concepts for the design and construction of the shoring and foundation work.
Supertall tower in the Toronto skyline
looking south towards Lake Ontario
Geometry and Design Challenges
The project site for The One building is
situated adjacent to one of the most builtup intersections in Toronto, Yonge Street
and Bloor Street West. The L-shaped
excavation measures 190 ft (58 m) by
154 ft (47 m) and ranges from 72 to 92 ft
(22 to 28 m) in depth, with one internal
corner projecting about 36 ft (11 m) into
the site along the west wall.
The design-build (DB) tendering
process allowed for innovative design
alternatives, which had to consider the
following constraints:
* No encroachment beneath the neighboring buildings to the south and west
* Existing deep basements limited the
space available for tieback anchorage
on the east and southwest
* Existing utilities beneath Bloor Street
West and Yonge Street on the north and
east
* Limited access around and under an
existing heritage building, which was to
be retained in place
AUTHORS
ARTICLE
* Limited space for the shoring on the
south and northwest sides due to the
proposed underground's proximity to
the existing buildings, and along the
east due to heritage building's proximity to an existing hydro duct
* Maximizing access for the proposed 10
to 11 ft (3.0 to 3.4 m) diameter structural caissons to be installed to depths
of 65 ft (19.8 m) below grade.
The geotechnical subsurface conditions at
the site consisted of generally shallow earth
fill underlain by glacial deposits down to
the Georgian Bay shale, located at a depth
of approximately 125 ft (38.1 m) below the
ground surface. The glacial deposits
contain stiff-to-hard varved silt and clay
extending to a depth of about 50 ft (15.2 m)
below grade, very dense-to-hard sand with
some silt from a depth of 50 to 120 ft (15.2
to 36.6 m) below grade and hard layered
clayey silt glacial till with gravel, cobbles
and boulders from a depth of about 120 to
125 ft (15.2 to 38.1 m) below grade.
The groundwater table is located
approximately 65 ft (19.8 m) below grade in
the cohesionless sands and silts. The
Shawna Munn, P.Eng., and Nadir Ansari, P.Eng., D.GE, Isherwood Geostructural Engineers, and Toben Jerry,
GFL Infrastructure Group
DEEP FOUNDATIONS * JAN/FEB 2020 * 87
DFI Magazine January/February 2020
Table of Contents for the Digital Edition of DFI Magazine January/February 2020
Contents
DFI Magazine January/February 2020 - Intro
DFI Magazine January/February 2020 - Cover1
DFI Magazine January/February 2020 - Cover2
DFI Magazine January/February 2020 - Contents
DFI Magazine January/February 2020 - 4
DFI Magazine January/February 2020 - 5
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