Precise bridge-moving operation key to Toronto’s Dufferin Street jog replacement

Called variously a planning oversight, and an example of railway company insolence, Toronto’s century-old Dufferin Street Jog was neither.

The detour, which once routed traffic around a railway bridge at Queen Street, was constructed so far out of town that it simply didn’t warrant much attention when it was built. As of November 2010, the jog was no more, replaced by a 72-metre tunnel in a $40-million, two-year project officially known as the Dufferin Street Jog Elimination CN/GO Transit Underpass.

“The masonry wall on the north side of the site has a date reading 1897 carved into the sandstone, so we imagine the original project could have been dated back to 1895 or 1896,” says Jim Schaffner, senior project engineer for structures and expressways with the City of Toronto.

“At that time, the intersection of Dufferin and Queen streets was a remote area in an industrial town outside the city limits and no one foresaw Dufferin becoming a major traffic artery.”

Modern-day projects designed to eliminate the jog have been considered as long ago as the 1960s, but recent development in the area spurred the construction of the new four-lane railway underpass. Work began on the project in July 2009.

Schaffner says that the north end of the development presented few challenges, but the job became more complex as it approached the south end in stages.

“The first stage forward was essentially an open excavation with no traffic control required to speak of,” he says.

“As we approached the south end, there were many more complexities, including the traffic on Queen and Dufferin and the rail bridges crossing the site.”

There were six rail lines on the rail corridor crossing the site, used by CN, CP, TTR and GO. The railways traditionally used the middle four. At any given time, three of the six rails were required to be kept open during construction.

Rail traffic was first diverted to the southern tracks as the northern bridges were shored up with temporary columns and tiebacks. The most northerly bridge was moved about 10 metres south to line up more closely with the other bridges. Rail traffic was then shifted to the northern tracks as work on the tunnel progressed.

“Ultimately, we had to raise the rail bridges by about three feet and support them on temporary trestles while we worked,” says Schaffner.

“To permanently support the bridge, we started with caissons that went down to the bedrock.

“The caissons were large in diameter, and there was a lot of groundwater at that location.”

The contractor had to excavate for the caissons inside a lining so as not to disturb the surrounding soil.

Next, a steel frame was constructed off-site to exacting tolerances set by the American Railway Engineering and Maintenance-of-Way Association. This frame was supported by the caissons.

“Getting the rail bridges to touch down on the pre-determined drop points was a significant challenge,” says Schaffner. “Once the new, higher railroad bridge was in place, the grades of the approaches to the east and west were altered for about 100 metres or so to accommodate the new elevation.”

The project also included construction of a park, using some of the historic limestone originally used on the site.

“One of the archival photos we have of the area shows the beautiful Gladstone Hotel, with an additional turret, in 1910,” says Schaffner. “My favourite construction photo shows the Gladstone in exactly the same position 100 years later. It gives the project a great sense of continuity.”

The project was designed by Delcan and built by Dufferin Construction Ltd. and Holcim Canada for the City of Toronto. McCormick Rankin Corp. was responsible for contract management.

Subcontractors on the project included: Core Excavation; HC Matcon (shoring/caissons); Harris Rebar; Dufferin Construction/Holcim Canada (formwork/concrete); Munro (precast); Central Welding/Ganawa Bridge Services (structural steel); AGI Traffic Technology Inc. (electrical); Bridge Tite (waterproofing); and Gazzola Paving.