Engineering Heritage: Integrating North America's Largest Façade Retention System with Support of Excavation in the United Bldg. Project-PPT Presentation

PPT Presentation

Pdf Summary

The presentation describes the engineering and construction of a façade retention system (FRS) integrated with support of excavation (SOE) for the United Building project at 481 University Avenue in downtown Toronto.<br /><br />The project required retaining the historic façade while demolishing the interior and excavating through typical downtown soils—fill, clayey silt, silty sand, clay and silt—to shale bedrock. Limited working space and overhead wires shaped construction methods. The exterior SOE combined large-diameter secant piles with street-level and basement micropiles. Interior FRS king piles were rock-socketed, and structural-steel trusses, transfer members, tie-ins and jacking pedestals connected the retention system.<br /><br />An estimated 20,000 metric tonnes of building load had to be transferred from 50 remaining columns, each carrying an estimated 340–460 tonnes. To reduce the risk of façade movement or system failure, engineers used a monitored, incremental jacking process. Hydraulic jacks, strain gauges and displacement gauges tracked load and movement across five jacking steps, repeated through multiple project segments. Columns were progressively loaded, separated—using different procedures for steel and concrete—and secured with load-transfer plates or adjustable shims.<br /><br />Excavation support included strategically positioned tiebacks and walers, plus shotcrete facing with double reinforcement mesh. High-early-strength shotcrete enabled some internal walers to be replaced with reinforced shotcrete panels.<br /><br />The presentation emphasizes the coordination of façade retention, excavation support and controlled load transfer under tight site constraints. It notes that the presenters’ opinions are their own and that DFI does not guarantee the information’s accuracy or endorse their recommendations.

Keywords

façade retention system

support of excavation

secant piles

micropiles

load transfer

hydraulic jacking

historic façade

downtown Toronto

tiebacks

shotcrete