Performance Based Excavation Support Design for Challenging Urban Site Geometry in Toronto, Canada-PPT Presentation

PPT Presentation

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The presentation describes the excavation support design for the EQ Bank Tower at 25 Ontario Street in downtown Toronto. The project involved an 18 m deep excavation for four underground parking levels beside a 100-year-old façade and neighbouring buildings.<br /><br />Site conditions included variable fill, glacial till and Georgian Bay shale. The shale’s high locked-in horizontal stresses could cause movement as excavation opened vertical rock joints. A further challenge was a gas main along the north and west boundaries: it was closer to the property line than records indicated, and Enbridge required access throughout construction and at least 300 mm clearance. Relocating the main was not feasible.<br /><br />For the north wall, the team designed a W150 spile shoring system installed using hydrovac, supported by five levels of hollow-core bar anchors. A king pile supported the slab and façade. Along the east side beside Toronto Community Housing, anchored shotcrete supported the soil, rock and neighbouring building loads; anchors were preloaded to limit movement, and line drilling helped create a clean excavation face.<br /><br />Construction issues included defective micropile casing threads and boulders that prevented some spiles from reaching their intended depth. Smaller steel pipes restored continuity through defective casing zones, while a panel sequence and conventional shotcrete addressed shallower spile installations.<br /><br />Monitoring used pile targets, inclinometers, extensometers and shape acceleration arrays. Spiles moved a maximum of 14 mm into the site; micropile movement reached 12 mm by project build-out. Neighbouring-building movement was negligible at about 5 mm. Overall, the shoring performed successfully, with movements around the site approximately 0.06% of the excavation height.<br /><br />Key lessons included the importance of clear communication, reliable monitoring to guide design adjustments, and timely, accurate utility information for developing efficient solutions.

Keywords

EQ Bank Tower

excavation support

Toronto

shoring design

18 m excavation

spile shoring

anchored shotcrete

micropile casing

gas main clearance

monitoring instrumentation