HERITAGE FAÇADE SUPPORT AND EXCAVATION SHORING – A MICROPILE CASE HISTORY-Paper

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The Canadian Westinghouse Building, a six-storey heritage structure at 355 King Street West in Toronto, was redeveloped as part of a project involving two residential towers and five underground parking levels. Its two street-facing façades were preserved in place while the rest of the building was demolished.<br /><br />A conventional large-diameter shoring system was impractical because of nearby gas mains, a major electrical vault, heavy traffic, and streetcar tracks that prevented lane closures. The project instead used a hybrid system of small-diameter Case 1 micropiles. Installed in two rows beneath a temporary steel façade-support frame, the piles also served as soldier piles for excavation shoring. They carried compression and tension loads from the frame and resisted lateral earth pressures. Welded steel tees supported timber lagging between piles.<br /><br />Restricted access required compact drilling rigs and careful utility protection. Where the electrical vault prevented micropile installation, the excavation face was supported with shotcrete, soil nails, and inclined rock spiles. Excavation reached its final grade in November 2016, with frost blankets installed beneath the façade. The temporary frame was to remain until the new structure could support the heritage walls.<br /><br />Monitoring showed acceptable shoring performance, with movements generally within the anticipated range. Façade movement reached a maximum of 38 mm away from the naturally stiffer site corner; although not predicted, it was judged acceptable by the structural engineer.<br /><br />The case demonstrates how micropiles can provide both façade-frame foundations and excavation support when urban congestion and utilities rule out conventional shoring.

Keywords

Canadian Westinghouse Building

Toronto heritage redevelopment

micropiles

excavation shoring

façade retention

temporary steel frame

soldier piles

utility constraints

shotcrete and soil nails

urban construction monitoring