Frost jacking created rockslide
A rock slide that closed Hugh Allen Drive between Versatile and Copperhead drives should be cleaned up by Tuesday night (March 5), with the road’s re-opening expected as well.
The road has been closed since early Sunday morning (March 3) when large chunks of rock came crashing down on the section of road that climbs high over the Versataille commercial area, connecting Aberdeen with Pineview Valley.
Dennis Luison, assistant streets manager for the city, said a geotechnical report shows the slide was caused by frost jacking.
“It’s just a freeze-thaw cycle,” he said.
“Water gets behind [the rock], cold temperatures freeze it, it just kind of jacks it out a bit.
“And, over time, that may cause some rocks to let loose.”
Luison said a rock slide of this magnitude is unusual, however.
He estimates a five- to seven-metre section of the rockface, up to five metres thick in some places, broke away.
“This is the largest we’ve had up there,” he said.
“Normally, it’s just a few small rocks.”
While there are rods drilled into the rockface in the area to hold it in place, Luison said slides are still “something that happens.
“Ice has a lot of power, so all the preventative measure to hold it in place, that can change,” he said.
To try to combat that, the city maintains a larger-than-average ditch along that section of Hugh Allan Drive.
It’s that catchment area that is taking longest to clean up, and which is keeping the roadway closed.
“We don’t want to open it until we can get the catchment area clean so it can hold more rock should it want to fall,” Luison said.
Once the road is clear, the city plans to conduct a full geotechnical assessment of the rockface to determine if other preventative measures need to be put in place.
A yellow Saturn was left at the scene of the slide on the weekend.
It was slightly damaged by falling rock, though nobody was injured.