April 16, 2010
FEATURE | Demolition/Environmental Engineering
Progreen Demolition tears down two 14-storey Toronto apartment towers
Another block of Toronto’s Regent Park neighbourhood is vanishing as demolition crews wrap up the takedown of two 14-storey residential towers and nine two- and three-storey townhouses.
The project, which started in December, is on track for completion in May, several months ahead of schedule. While cooperative winter weather has helped smooth the way, the demo contractor has put a sizable crew and big fleet of equipment onto the job to ensure a speedy takedown.
The demolition started with asbestos abatement in the two towers, followed by stripping interior finishes. Three high-reach Liebherr cranes (“basically excavators with long booms”) with concrete cutting shear attachments do the bulk of the tower demolition, but the long-boom cranes only reach as high as the 11th floor. Small excavators and bobcats are hoisted to higher floors for the take down, says Paolo Provenzano, president of Progreen Demolition Ltd.
Demolishing upper floors takes about a week, starting with removal of interior construction materials and finishes, and then cutting rebar before lowering the concrete slabs, he says. Temporary shoring is required.
Progreen must abide by regulations concerning noise abatement and dust mitigation — the latter involves spraying the demolition with a calcium/water mix.
Provenzano says 90 per cent of the block’s demolition debris will be recycled. The concrete, for example, will be crushed on site and used as backfill in the new residential development’s road network. Rebar, meanwhile, will be shipped to a steel plant for recycling.
Unrecyclable construction debris includes roofing materials and some of the buildings’ interior finishes.
Progreen’s job also involves the removal of about 10,000 tons of contaminated soil — some of which is laced with hydrocarbons, says Provenzano.
Prior to demolition, Progreen had to retain an engineer to assess the structures of the two 14-storey towers and supervise the demolition — a requirement under regulations in the Ontario Building Code.
Mike Guirgis, principal of the job’s structural engineer PETRA Consultants Ltd., says for demo jobs like Regent Park, his role starts with scanning original condition plans of the buildings.
He says the problem was that some of the details on the original 60-year-old plans weren’t legible. “We had to cut/break some slabs to verify that those plans were the actual construction version ones, not preliminary ones as is often the case. Based on revealed information we prepared a report describing the structural system of the building, including some produced plans of existing conditions. That led us through a demolition methodology that best fit the structures and site conditions.”
PETRA is also responsible for monitoring Progreen’s demolition, ensuring the contractor follows the removal procedure in sequence and that structural integrity is not compromised during the process.
Weather and wind play a role in what gets done and when, says Guirgis, adding he is responsible for providing progress reports throughout the demolition to all parties involved, including the city.
The first phase of demolition at Regent Park started in 2005. The neighborhood’s redevelopment is expected to be completed in the next five or so years. Regent’s Park was on the cutting edge of planned residential communities when it was constructed in the late 1940s and 50s.
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