Stabilizing Slopes
Holding soil in place with concrete mats, hydraulically applied materials, rockfall netting, and grout .
From the mountains to the ocean, slope stabilization is an ongoing erosion control activity throughout North America as slopes present ongoing dangers due to usual erosion, unanticipated weather activities, or construction jobs.
Watch for Falling Rocks
Colorado hosts many notable areas, but there's one that has always made state officials nervous. That area—located west of Denver—is a 2-mile stretch of Interstate 70 between Georgetown and Silver Plume. Its notoriety is rooted in the fact that many people have been injured or killed by rocks sliding down the steep slopes of Georgetown Hill in the heavily trafficked area, notes Mick Muller, a chief designer and project manager for the Yenter Companies in Arvada, CO.
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PHOTO: PROFILE PRODUCTS |
One rockfall from the 40% slope in April 2004 took out a 12-foot-high fence on a slope above the Georgetown Loop Overlook. Muller's company was assigned the task to create safer conditions through the installation of two rockfall fences: one to replace the damaged fence and another located higher up on the slope in an effort to slow the progression of falling rocks before they reached the lower fence.
Working through the winter of 2004 to ensure completion before the spring 2005 runoff caused more rockfall, the company used helicopters, a capstan wrench, and a pulley system and also carried materials by hand up nearly 400 feet to build a solution favored by the Colorado Department of Transportation for the rockfall mitigation project: attenuator fences.
"It's a little different than most rockfall fences in that rocks hit the fence and the bottom is not restrained, allowing the rocks to continue to slide down the hill if they have enough energy," Muller explains.
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PHOTO: PROFILE PRODUCTS |
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PHOTO: PROFILE PRODUCTS |
When the April 2004 rockfall took out the previously installed fence, it was because the rocks sliced the wire ropes. The installation of metal sleeves over the wire ropes of the anchors is designed to prevent that by spinning.
The fences were installed over rockfall chutes. The Yenter Companies used anchor bolts—drilling them 6 feet deep for the columns—from the Williams Form Engineering Corp. The columns were anchored into the holes with concrete and the metal netting was then attached. In total, the project cost $400,000.
Roadway Construction in Ontario
In another slope stabilization road project in Ontario, Canada, a highway reconstruction effort of 15 to 18 kilometers along a stretch of Highway 26 was undertaken to level out hills in an area east of Owen Sound, ON. The erosion control project began in May 2005 and was expected to take place through the autumn months.
Rick Collins, president of InstaGreen, the Ontario-based company that performed the work, says the roadway construction was a multifaceted project with ditches and fairly steep slopes of 2:1, as well as poor-quality clay soil. "There also were places where the soil slopes terminate into a rock face at the top and bottom, so I tried to reason with the general contractors that straw blanket was not going to be practical nor the best-performing way to go because it was going to be so difficult to do it with that product," he says.
For erosion control and turf reestablishment, Flexterra from Profile Products was used. Flexterra is a flexible growth medium containing wood and synthetic fibers and additives, including tackifiers to help bond to the soil. There was a concern about using some types of materials near the area's many environmentally sensitive rivers, creeks, and bogs; unlike traditional erosion control blankets, Flexterra has no netting, staples, or mesh in which wildlife can get caught.
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