Performance Based Excavation Support Design for Challenging Urban Site Geometry in Toronto, Canada-Technical Paper Upload

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The EQ Bank Tower project in downtown Toronto required an 18 m excavation for four underground levels while preserving a historic brick façade and protecting nearby buildings, utilities, and foundations. Two major challenges shaped the excavation-support design: a live gas main only 450 mm from the façade, leaving little room for shoring, and deep excavation into highly stressed, expansive shale beside a sensitive 12-storey apartment building.<br /><br />A performance-based approach, supported by monitoring and the observational method, enabled the team to adapt the design to site constraints. Near the gas main, hydrovac-installed steel spiles and anchors supported the upper excavation. Inside the façade, low-headroom micropiles served as both temporary columns and lower shoring elements, with the building’s P1 footprint preserved. Along the neighbouring building, anchored shotcrete, preloaded anchors, line drilling, and anchored channels protected the rock face and existing caissons.<br /><br />Construction challenges—including boulders that prevented some spiles from reaching their planned depth and defects in micropile casing threads—were managed through staged excavation, supplemental support, and additional monitoring. Instrumentation tracked wall and ground movement, allowing the team to adjust anchor loads and avoid unnecessary remedial work.<br /><br />Measured movements remained modest: the spile wall moved up to 14 mm, façade micropiles up to 12 mm, and the east rock face up to 7 mm. Surveying showed less than 5 mm of cumulative movement in the neighbouring building.<br /><br />The project demonstrated that complex, space-constrained excavations can be managed through adaptable design and reliable monitoring. Key lessons included the importance of clear, ongoing site communication and obtaining accurate utility-location information early enough to preserve design options.

Keywords

EQ Bank Tower

Toronto excavation

deep excavation

excavation support

historic façade preservation

gas main constraint

micropiles

shoring design

monitoring instrumentation

observational method