August 30, 2012

MCCORMICK RANKIN

The Sixteen Mile Creek bridge in Oakville, Ont. is a twin 275-metre-long, 35-metre-high, five-span post-tensioned precast concrete I-girder bridge.

FEATURE | Roadbuilding

Building Bridges

Sixteen Mile Creek bridge spans new horizon

DAN O’REILLY

correspondent

Building a new bridge spanning one of Halton Region’s most scenic waterways was no small undertaking, financially or structurally.

The Sixteen Mile Creek bridge at Dundas Street in north Oakville is a twin 275-metre-long, 35-metre-high, five-span post-tensioned precast concrete I-girder bridge on concrete piers, with a 5.2-metre-wide space between the north and south sections.

“They are totally separate, with their own sub and super structures,’ says Joseph Choi, the region’s transportation design and construction manager.

Both have three vehicular lanes each, as well as bicycle/ pedestrian lane, he says.

At a cost of $71 million, the bridge is one of the single most expensive transportation projects ever undertaken by the region and one of the longest. It took five years to complete the project which was divided into two phases.

Extensive environmental protection measures were also needed to protect the creek from the construction activity which included the new construction, demolition of the existing structure and tunnelling under the creek, says Choi.

“No in-stream work could be conducted between September 16th and June 30th.”

The new bridge replaces a 1960 four-lane steel truss bridge which didn’t have the capacity or the structural strength to accommodate a current traffic volume of 39,000 vehicles daily, says Choi.

He emphasizes that number to explain the complexity of demolishing the old bridge, constructing its replacement and keeping traffic moving, almost simultaneously.

The long construction schedule stems from the sequencing of the project which was divided into two contracts to minimize, as much as possible, traffic gridlock, says Choi.

Grascan Construction was the general contractor for the $26-million, Phase 1 south section. Dufferin Construction oversaw the $45-million Phase 2 north twin contract which also encompassed a tunnelled 1.2-metre-diameter watermain and a twin 750-millimetre forced sanitary sewer which is suspended on the bridge’s two halves. McCormick Rankin, a member of the MMM Group, was the consulting engineer.

In 2007 Grascan started building the south side of the new bridge, while maintaining the old bridge to the north to ensure traffic flow. When the south section was opened in early 2009 the designated bicycle and pedestrian path was used as a temporary fourth vehicular lane.

This was an interim measure to keep traffic moving.

As Grascan was wrapping up its work, Dufferin Construction was marshalling its workforce on site. The first item in its contract was to demolish the 1960 structure which was necessary so construction of the north twin could begin. J.L. McConnell Contracting was the demolition subcontractor.

Several safeguards had to be in place to protect the creek from possible falling debris, says McCormick Rankin senior project manager Robert Rook.

A catcher comprised of steel bins with splayed sides and a woodfloor was placed below the old trusses, with fabric drapes hung from the trusses to direct debris into the catcher, he says.

Although the demolition had to be finished before work of the north twin section could begin, it wasn’t a complete gutting of the old structure.

“The new north bridge piers are founded exactly on top of the existing 1960 truss bridge pier foundations.”

As for the other work, Newmarket-based Technicore Underground Corporation used a tunnel boring machine to construct a tunnel about eight metres underneath the creek to carry the 1,200-millimetre watermain. This required the excavation of 47-metre-deep shafts on both banks.

Dufferin sub-contractor, D’Orazio Construction was responsible for the installation of the twin 750-mm forcemains which are supported between the girders on a carriage system bolted into the bottom flanges, says Rook.

While the new bridge is now operational, some work remains. During construction the popular Lions Valley Park, which is on both sides of the river underneath the bridge, had to be closed for the safety of the public. Restoration work, which includes the construction of a pedestrian bridge, is now underway, says Halton’s Choi.

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