Second phase of Hwy. 104 twinning now complete

The second phase of Hwy. 104 twinning in Antigonish, N.S., was completed recently, with eight kilometres of new four-lane highway.

The $86-million project includes two roundabouts, three underpasses and two 300-metre-long bridges spanning the South River in northeastern Nova Scotia.  CBCL Limited was the design engineer of the project.

The twinning project began with the construction of the two South River crossings — steel box girder designs, each on three piers.  General contractor was Nova Construction Co. Ltd. of Antigonish and Harbourside Engineering was the designer.

"Bedrock was highly variable Karst (unusual rock formations), and therefore different pile configurations were required," explains Angus Gillis, project engineer at Nova Scotia’s Department of Transportation and Infrastructure Renewal.

"In some areas we had weathered mudstones intermixed with layers of limestone and outcrops of gypsum," he says.

While drilling, often the drill bit would "fall several metres as a result of hitting a void," Gillis points out.

Also challenging about the landscape were watercourses that "disappeared into the ground" and other places where water simply "came to the surface."

The pile foundations, says Gillis, were comprised of pipe piles filled with reinforced concrete "rock sockets" measuring seven to eight metres.

The sockets are designed to "bite into or bond to the surrounding rock. The casing (pipe) would be drilled to the rock and then drilled another 0.6 metres into the rock to seat the casing.  The socket would then be drilled in the rock and the bit retracted through the casing."

Gillis says that pile shaft lengths were up to 20 metres.  There were more than 373 piles measuring a total of 6,300 metres.

He says slope stability structures were used in front of the abutments and consisted of similar pile foundations and pile caps.

Engineer Sheena Berthiaume says the four-year project came in about $2 million over the original budget which is "really quite good when you are looking at a project over $84 million."

The Hwy. 104 twinning project was done in two phases for a total of 15.5 kilometres of new four-lane highway. Phase one includes three interchanges — each with two roundabouts — four overpass structures, one underpass, two bridges and a tunnel, says Berthiaume.

Phase one started in 2009 and was opened in 2012 for about $75 million.