British Columbia is home to some of the most picturesque landscapes in Canada. But with large amounts of precipitation, lush vegetation and mountainous terrain, it’s also one of the most landslide-prone.
In fact, one of the country’s largest recorded landslides occurred east of Hope in 1965. The landslide resulted in about 47 million cubic metres of rock stretching across three kilometres of Crowsnest BC Highway 3 (imagine 18,000 Olympic size swimming pools filled with rock and you’ve got the idea). Ongoing weathering processes caused the mountainside to weaken and collapse, with serious consequences.
Since then, our team of engineering geologists and geotechnical engineers have enhanced measures for reducing the impact of landslides.
Active Measures reduce the impact of a landslide when it happens. Examples include:
- Trench: a hole dug at the slope’s bottom, which prevents falling rock and debris from landing on the road.
- Retaining wall: a solid structure designed to keep falling rocks and debris from reaching the highway.
- Catch fence: designed to be flexible and absorb energy, fences are constructed using steel posts and steel net panels. The net panels can expand several metres to absorb the impact of falling or rolling rocks.
- Slope mesh: draped steel wire mesh directs rockfall into highway trenches. The slope mesh is suspended at the top of the slope from a system of steel bars, or anchors, drilled into the rock with support cables. Rolls of mesh are then lifted into place by helicopter or crane, then unrolled and stitched together to form one continuous protective blanket.
Preventative Measures reduce the risk of a landslide happening. Examples include:
- Drain holes: horizontal holes are drilled into the slope and lined with drain pipe to help relieve built-up water pressure from underneath the surface.
- Trim Blasting: removal of rock using closely spaced drill holes loaded with explosives. Generally the holes are drilled by workers suspended from ropes using handheld drills called “pluggers,” but drilling may also be performed out of cranes or man-lifts with bigger drills.
- Shotcrete: Ever wonder what that clay-like coating is over rock walls? It’s special fluid-like concrete, sprayed on to support loose and fractured rock.
- Rock bolting: stabilization of rock using tensioned steel bars. Holes are drilled into the rock at locations where there is potential for blocks of rock to fall off the slope. Bars are then cemented into the rock to hold the large blocks into place. The drilling is usually performed from a suspended staging called a “spider,” but may also be conducted from cranes or man-lifts. Each rock bolt can support several tons of rock.
- Berms: masses of blasted rock or heavy boulders are placed at the base of a slope to help support and prevent sliding.
- Rock scaling: removal of loose rock. Workers, nicknamed “Rock Scalers,” access the slope suspended from ropes. Scaling is usually the first activity conducted on a rock slope to remove any loose material that presents a hazard to traffic and workers.
Some of these measures can be seen from the highways, while others are hidden; all are working to keep travellers safe. Next time you’re driving through a mountainous section of highway, impress your friends by listing off some of the ways the looming rock and debris is kept in place. Then again, maybe just admire the picturesque landscape.