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cheak rocks

Slide site gets 'cheak-up' By Chris Woodall The site of last May's massive rock slide in the Cheakamus Canyon which closed Highway 99 for much of the summer is being monitored for potential movements. "There have been no movements to date," says district engineer Jacques Dupas of the B.C. Ministry of Highways. The ministry has been visually monitoring the remaining slab of rock at the site and is planning to install a hi-tech monitor in April. Standard survey equipment is being used now to eyeball shifts in the rock slab, Dupas says, but a 22-metre fibreglass rod will be inserted into a drill hole so that Highways staff can "listen" for the slightest untoward shift in the rock. "It's much more sensitive," says Dupas. The drill hole will extend completely through the rock slab and into the stable bedrock, Dupas explains. The rod will be hydraulically attached to the back of the drill hole, with a series of electronic monitors attached to the front of the rod that are connected to a telephone line in Burnaby to tell of any up, down or sideways movements. Information can be collected at set intervals during the day — every minute, every 10 minutes or once a day, for example — that will be transmitted to the home office to produce a graph of movement. And there will be some movement. Changes in heat during the day will cause minor "diurnal variations" or twice-a-day movements that are naturally occurring, Dupas says. "It's definitely a large rock mass," Dupas says of the monitored rock slab. "This is another level of security. It's prudent to be monitoring it when we've had the magnitude of the previous slide." When the major slide occurred last May 19, 45,000 cubic metres of material eventually cascaded onto the highway, closing it on and off for a week as crews tried to haul away boulders the size of houses. Work done on the rock slab as part of the clean up and repair included drilling a series of two-inch-wide holes several metres into the rock across crack lines so that water in the cracks can drain away instead of building up enough water pressure to lift the slab off the bedrock and down to the highway, Dupas says. Should the worst happen and the slab let go, Dupas reminds motorists that the "sizeable berm" thrown up by earth moving equipment at the slide site is designed to catch any anticipated activity.