Shoring Up Infrastructure
Gabions and hard-armor solutions
From shoring up aging infrastructures to redirecting water flow to offering an artistic appearance, gabions and hard armor have become an increasingly important tool in North America’s erosion control efforts.
Municipal officials in Enniskillen, ON, have been slowly rebuilding aging bridge structures since the early 1990s using precast concrete box structures manufactured by International Erosion Control Systems (IECS). Enniskillen has worked on one bridge a year for the last several years using IECS concrete gabions.
“The design has changed slightly, but we’ve been using them for erosion control at least since the 1990s,” says Ray Dobbin, township engineer.
The concrete gabions combine noncorrosive interengageable stackable concrete blocks with transverse ducts and are available in various sizes. The gabions are teamed with geotextile cloth.
Because the product has proven itself reliable over the past decade, Dobbin continues to use it in various applications. “We’ve been using them as end walls,” he says. “We like the drainage holes and the curve on top. We also use them on roadwork. We like that with them being precast, we can construct a small bridge in less than a day.”
Dobbin says the township has used the concrete gabions as wing walls on precast structures, fastening down one layer of the blocks across the top of the structure and using that as an end wall across the bridge to support the cover over the bridge.
In choosing the gabions for the project, Dobbin considers structure. “That’s because it’s on a road, as opposed to a farm culvert in a field along a road. Structurally, the base blocks are on the bottom and then we build the cinder blocks up with the curve,” he says. “We generally don’t go too high with them—maybe three or four high—and with those features, it makes it easier. They work better building the wall and supporting the wall and the traffic. It stands up to the load on the road.”
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Photo: Utah DOT |
| Preparing to install A-Jacks units |
Drainage issues for the backfill in the road also are a concern, Dobbin says. “The precast concrete will have joints in it. We wrap them with filter fabrics, and that helps to drain the backfilling behind the structure. Because we’re in clay soil here, we backfill with granules to keep it well drained in behind; that works out well.”
Dobbin says he doesn’t like to put any longer culverts in than he must. “We want to put the minimum amount of culverts in and make use of that for the traffic portion on the road. That makes it important for the end walls to be able to stack them and keep them as straight up and down as we can to maximize the road width. These stack very straight and we’re able to maximize that. Because of their design, we can hold up that embankment on the wall fairly straight up and down, get a retaining wall, and put a shorter bridge in.”
For municipalities on limited budgets, Dobbin finds the precast structures cost-effective. “Our concern is we can take a bridge out and replace it with a precast box and these precast concrete gabions,” he says, adding that can usually be done within a week.
“We can take the bridge out Monday, set the precast structure on Tuesday, set the wing walls on Wednesday, the backfill on Thursday, and Friday we clean up and traffic is OK for the weekends,” Dobbin says.
The time benefit is key, Dobbin points out. “With precast, we know what we’ve got to do, so we get it all ready. The blocks come and we stack them and we’re away. We don’t have a bridge down half the summer or for a month.”
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