Bay Street demo requires ingenuity, consultation

A complex demolition job currently underway in tight quarters on a high-density block on Bay Street in downtown Toronto is proceeding smoothly thanks to careful planning to mitigate disruption, regular consultation with stakeholders and strategic use of technological innovations.

PCL Constructors superintendent Andrew O’Brien took time off the job recently to explain the scope of work and the innovative techniques and machines being employed to get it done.

The existing block at 700 Bay is currently home to an office building next to a 25-storey residential tower, and until recently, there was a two-storey podium covering about 25,000 square feet attached to the residences on top of five levels of underground parking. The developer KingSett Capital decided to knock down the podium, demolish the parking garage and rebuild by erecting a new rental building on a small footprint that would rise 31 storeys, with a six-storey overbuild extending over the existing residential building.

It’s essentially five projects in one, said O’Brien.

“It’s complicated,” he said. “If you imagine the new tower coming up is one project, the overbuild is another project, because you have to extend the elevators another six floors, and the demolition on the roof, and all the sidewalks is another project, the ground floor renovations is another project, so there are like five projects.”

The worksite is a block bounded by Bay, Elizabeth, Gerrard and Walton streets.

There are two demolition jobs — one at the podium site and the other on top of the existing residential building. There is a pool, parapets and other structures on top of that building that have to be removed before the overbuild is constructed. PCL is working with Priestly Demolition on the demolition jobs.

Given the tight space, and such sensitive neighbours as the Hospital for Sick Children, two luffing cranes that move vertically will be employed instead of regular hammerhead cranes, said O’Brien. The cranes are owned and operated by formwork subcontractor Structform.

One was installed May 18 on the west side and will climb with the structure and the other will go on top of the existing building June 9 or 10.

“One that’s on the roof, the overbuild, there’s a very big jib on it,” he explained. “The reason you need a luffer is because Sick Kids is so close to us. If we had gone with a hammerhead crane it would have spun into Sick Kids.”

Work on the 32-month job started last September with cut and cap work done on the podium to remove and reroute electrical and other services to ensure safety and continued use by existing tenants.

Excavators worked on the podium site to take apart the parking garage and at each level tie-backs were installed at vertical angles to hold the earth in place. Then a 100,000-pound caisson machine was lifted in place by a 400-tonne mobile and the caisson machine set to work drilling down into bedrock ­— about 600 to 900 millimetres deep, O’Brien estimated — and installing 49 caissons to support the new residential tower.

The demolition team is aiming to avoid chipping to get rid of the concrete on top of the existing tower and so robotic demolition equipment that uses a crushing technique will be lifted to the roof. The spec sheet for the remote-controlled Brokk 160 demolition machine boasts it hits “frighteningly hard” at over 406 joules at the tip.

O’Brien said another technique being considered to loosen the concrete is to use a chemical cracking technique. Holes would be drilled into the concrete, chemicals poured in and capped, the chemicals would expand over 24 hours and the cracked concrete could be easily removed, mitigating disruption of the neighbourhood.

The new residential tower will go up directly next to the existing building to provide stability, said O’Brien.

Also providing reinforcement to the existing building will be carbon fibre strips that will be glued to existing beams by a team from Freyssinet, he explained — they are only 1.4 millimetres thick but extremely strong.

Careful planning of the various teams of trades is required, O’Brien explained, noting mechanical, electrical, demolition and concrete workers have been onsite recently alongside eight or nine PCL staffers — about 75 workers in total currently with many more to come.

“We’ve got the trades lined up so there is a nice flow so they can get in and out of the project nice and easy,” O’Brien said.

The crews have to adhere to city noise bylaws and special permits are required for special jobs such as the recent installation of a crane.

Every day starts with site meetings at 6:30 a.m. to plan the day and there are regular meetings with other stakeholders, including Sick Kids, he said.

“The biggest thing on this project is communication,” he said. “There are a lot of stakeholders.”