Innovations and Challenges During Urban Development - Shoring and Foundations of Canada's Tallest Residential Building-Paper

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The paper describes the shoring and foundation design for The One, an 85-storey, 306 m residential tower at Toronto’s crowded Yonge and Bloor intersection. Its deep, L-shaped excavation and restricted footprint were complicated by nearby buildings, utilities, deep basements, a heritage façade, and the need to keep access available for foundation construction.<br /><br />Ground conditions and groundwater required an interlocking secant-pile cutoff wall extending into bedrock. The team evaluated tiebacks, internal bracing, a partial top-down scheme, and a heavily anchored “supercorner” before developing a hybrid solution. The final system combined tieback anchors, internal corner bracing, a temporary South-side slab, and micropile-reinforced shotcrete shoring near the heritage building.<br /><br />Foundations included large-diameter drilled shafts socketed into rock. Many were installed from the excavation base, with some positioned as close as 0.3 m from the shoring. Because vibratory casing installation could affect the shoring and adjacent structures, construction proceeded in stages, with real-time monitoring and test installations used to assess risk. Inclinometers, surveys, façade and building monitoring, and vibration sensors showed that movements remained acceptable; the vibration installation method had minimal impact on shoring performance.<br /><br />Frost caused a more significant challenge. Thin shoring walls moved more than thicker sections, requiring insulation, active heating, and berm backfilling. Some frost-related movement later recovered as temperatures rose or heating was applied.<br /><br />Key lessons include the value of design-build alternatives for constructability, the drawbacks of advancing shoring design before the permanent structure is finalized, and the need to account for frost protection—especially for thin walls. Overall, the project demonstrates how adaptable design, staged construction, and performance-based monitoring can manage complex urban excavation risks.

Keywords

The One

Toronto

shoring design

foundation design

secant-pile wall

deep excavation

tieback anchors

micropile shoring

vibration monitoring

frost protection