Boulders coming loose from Maley Drive extension caused by cracks, freeze-thaw cycle

Drivers along Sudbury's Maley Drive extension may be noticing a growing number of boulders falling from rock faces along the route of the roadway.

Motorists who take the Maley Drive extension in Greater Sudbury may be noticing a growing collection of boulders accumulating along the side of the rock faces.

Officials with Greater Sudbury say the extension was built to accommodate the falling debris, which is caused largely by the same factors that lead to potholes on roads.

David Shelsted, the city’s director of engineering services, said when about one million cubic metres of rock was blasted during construction of the extension, it created widespread cracks in the rock faces, which reach as high as 25 metres.

When water gets inside the cracks, freezes and then thaws, it loosens the rock, eventually causing boulders to fall.

Shelsted said the extension was designed knowing that debris would accumulate over time.

“We followed the Ministry of Transportation of Ontario’s good design guidelines,” he said.

“The higher the rock cut, the further away from the road it should be.”

Drivers can see that lower rock faces are closer to the road, while the highest are much farther away, he said. That’s to ensure that falling rocks have plenty of space and stay safely away from the road.

“You’re expecting some rocks to fall off -- that happens through the natural freeze-thaw cycles,” Shelsted.

Force of Mother Nature

“It’s incredible how much force Mother Nature has and the size of rock that can be moved.”

While the rocks are accumulating, he said they don’t expect to have to remove them any time soon unless they become a hazard at some point.

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“If the rocks were to show up a little bit closer to the road (and) there might be a chance of a passing vehicle pulling over to the shoulder and striking it, well then we would look at cleaning it,” he said.

“Or if it were to … clog up a ditch (or) get too close to the road.”

The rock fall was heavier when the extension first opened, but is evening out as it settles over the years. But, Shelsted said, the design takes into account the possibility of even a very large boulder falling, as happened several years ago on Regent Street.

They regularly inspect the rock faces on Maley, as well as others on the city.

“All rock faces continue to have movement as the freeze-thaw cycles come through,” he said.

The Maley Drive extension officially opened in 2019 and cost $80.1 million to build, with the city contributing $26.7 million. It runs from Falconbridge Road to Frood Road, allowing heavy trucks and other vehicles to bypass Lasalle Boulevard and the Kingsway when getting across town.

Recent data showed it has reduced traffic on Lasalle by more than 8,600 vehicles a day and reduced truck volume by 30-40 per cent, including a 75 per cent reduction in heavy transport trucks.