For municipal public works and road officials, failing slopes pose a whole set of complex legal, technical, engineering, and environmental issues, not the least of which is addressing the fears of adjacent homeowners.
A test project completed late last fall by Peel Region may provide some solutions to those challenges.
"We needed to come up with something fast, permanent, basic and environmentally sensitive," says regional project manager Serguei Kabanov, about a problematic slope along Highway 50 in the Town of Caledon, Ont.
First identified as a major problem area in 2013, the approximately 11-metre-high, (36 feet), 220-metre-long (771 feet) slope was experiencing failure, surface erosion and movement, with the soil sliding towards the ditch and the road. Not only did the fallen material have to be cleaned out of the ditch numerous times, two homes are near the slope.
"They did raise multiple concerns," says Kabanov, when asked if the homeowners were worried.
Geotechnical studies indicated poor drainage and inadequate erosion protection as the source, he says.
A "very basic, simple, and inexpensive approach" was presented to regional officials at a seminar in early 2014 by Waterloo-based Envirolok Vegetated Environmental Solutions.
"The idea was to re-shape the slope with vegetated bags which would eventually over grow with seed and weeds," says Kabanov, suggesting the methodology is not unlike how sand bags are used to control flooding rivers.
Vegetated bags filled with a homogenous mix of sand and compost, 60 per cent concrete sand, 35 per cent topsoil, and five per cent compost are stacked in a particular order at a certain orientation and connected with pins. The bags are made from a specifically designed non-woven geotextile that will not rot or mildew, is non-biodegradable and are resistant to damage from insects and rodents.
"The slope to be achieved dictates the orientation and placement of the bags. This is not a take-off-the-shelf approach," says Kabanov, explaining Envirolok’s own engineer, Inspec-Sol, has to prepare drawings and specifications.
Not wanting to wait any longer and face the possibility of a slope failure, the region selected Delcan/Parsons as its consultant. Detailed design was completed by the end of last summer and then a tender was issued in September with a clause that the project had to be completed before Nov. 28. Cambridge Landscaping Inc. was the successful bidder.
As the Envirolok system had never been used before in Peel and was new to both the consultant and the contractor, the region opted for the three different stabilization methods.
A fairly gentle portion was re-graded, while an armour stone retaining wall was erected for the steepest section.
After French drains were installed, the third area — the one furthest away from the homes — was stabilized with approximately 1,000 prefilled Envirolok bags. Connected to the ground with pins, they were placed in staggered order from the bottom of the hill to the top, backfilled and then hydro seeded — all within four days.
"The bags will provide immediate structural stability," says Envirolok General Manager Jay Morgan, who oversaw the operation and even helped place some of them.
Although access to the work site was limited due to the steepness of the slope and no access whatsoever through private property, there was no impact to passing traffic, says Kabanov.
"Constructability of this slope was very carefully thought out during the design stage," adds Kabanov, who credits senior Peel managers in several different departments for approving the pilot project.
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