Façade Retention Meets Earth Retention in the United Bldg. Project

In the heart of downtown Toronto, a full city block at 481 University Avenue and 210 Dundas Street West has become the site of one of the most complex heritage preservation efforts ever attempted in North America. The development of the United Bldg., a 50-storey mixed-use tower, required the complete in-place retention of two culturally designated façades: a 9-storey Beaux-Arts structure built in 1928, and a 10-storey Modern Classical building completed in 1961. The City of Toronto By-law 1393- 2017 designated the façades of both 210 Dundas Street West (Maclean Pub- lishing Company Building, 1928) and 481 University Avenue (Maclean- Hunter Building, 1961) as heritage sites due to their architectural, historical and contextual significance. Regulations imposed by this bylaw prohibited dismantling or relocating any part of the heritage façades. All original finishes brick, stone, concrete and steel - had to remain undisturbed and fully supported throughout construction. At 10 storeys tall, the façade retention system (FRS) designed for this project was a monu- mental engineering and construction marvel that was unprecedented in the industry. The complexity of this project was only amplified by the spatial lim- itations imposed. Dense urban infra- structure - including streetcars, sub- way tunnels and congested utilities not only restricted the available options for the FRS design but also imposed stringent monitoring criteria. The solution selected needed to restrict ground settlement to fewer than 3 mm (0.1 in) and façade movement of 15 mm (0.6 in). This led to the development of a highly integrated hybrid support system, merging elements of the existing structure with the FRS and the support of excavation (SOE) design to allow four levels of underground construction beneath the retained façades and structure. On the United Bldg. project, Canadian specialty contractor Green Infrastructure Partners was responsible for delivering the demolition, shoring scopes and façade retention. This included the full demolition of two brick buildings and the partial demolition of 210 Dundas Street West and 481 University Avenue. The shoring scopes executed the full deep foundation system including secant piles, micropiles, caissons, tiebacks, walers and shotcrete. The façade retention entailed the fabrication, supply and installation of all FRS steel and connections, as well as the jacking of the retained structures onto the new foundations.