The Faces of Retaining Walls
Designers discuss drainage, subsoils, settlement, cost, and appearance.
For some people, appearance means everything.
While a retaining wall has always served the purpose its name implies, these days, those who build them are concentrating on looks as well as substance.
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Photo: Rinker |
| The industry trend is moving toward more natural-looking retaining walls. |
“Appearance is everything,” Glen Reddemann says of retaining walls. He’s vice president in charge of operations for TPC Landscape in Burnsville, MN. “We’re a higher-end company, so functionality is one thing, but appearance is everything,” he adds. “We like to structure a product that is maybe a little bit more unique than just a gigantic modular wall.”
For that and other reasons, his company has turned projects down. “They may spec a product we don’t really want to use or put our name behind,” he says. TPC Landscape favors Interlock Concrete Products or Anchor Retaining Wall Systems for its retaining walls.
Reddemann says the trend for retaining walls for the past two decades has been modular block walls that look more like a concrete block. “They have turned the corner and are trying to look more natural, which has been exciting,” he says. “People don’t necessarily want to use natural stone, or there may not be a place where you can apply natural stone. You can use a lot of other products that have multiple sizes and pieces and roughed base that look more natural. It beautifies the area more than just a concrete wall that has no aesthetics in appearance whatsoever.”
As for the engineering aspects, Reddemann says structural considerations often determine the options his company has available when building retaining walls. The subsoils—heavy clay or sand—in combination with such factors as nearby parking lots or residential buildings determine the products his company will use. Other factors include the load rates and whether the wall will be structural or ornamental.
Regarding heights, Reddemann believes “you can just about engineer any product to go any height you want. As long as the engineering specs come out, we’ll build it. I don’t believe that there’s a maximum height to really any product.”
He notes soil type is another engineering consideration that affects the strength and height of a wall. “The soil conditions under the wall and behind the wall may call for amending prior to doing anything,” he says. “But whatever that may be, it’s done pre-construction. They can take any project that’s engineered and put it up, based upon what you have to do in amending soil. Maybe they want to lay the wall on a concrete pad. We have a lot of frost issues we deal with. The heavier soils, like the clays, move more frequently than sand. We’ve got just about every kind of material you could ask for, from rock to sand to heavy clay to loam.”
Whether soil is used from onsite or imported depends on the development, Reddemann says.
“If they’ve got good material or the engineering specs say to use the material that is there, we don’t import it if we don’t have to because the additional costs incurred would be great, especially with the current costs of trucking,” Reddemann says. “For the most part, we like to use the product that is there.”
Reddemann says his company likes to use clear crushed limestone for compaction behind the wall.
“The majority of that is to disperse that hydrant pressure, the water limitations from the soil behind you,” he says.
Reddemann believes that for addressing drainage issues, drainage swales are always the best approach. “If the grade is done correctly, the majority of the water will either run off the wall or come over the top of it; some will leach through or run through the drain tile system you place in the back,” he says.
“The best idea anybody ever came up with is keeping water away from areas you don’t want water. Drainage swales being cut in front of the wall so the water isn’t coming to it is your best bet.”
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Photo: Rinker |
| Retaining walls may be aesthetically pleasing as well as functional. |
Slowing the Waves
Wall appearance was the primary reason Mark Thomas’s company was chosen for a recent concrete retaining wall project in the Flathead Lake near Glacier National Park in Montana. “Because it is concrete, it can be stained, and the number of stains available are phenomenal—they’re water-based, oil-based, acid-based—and it depends on what you want to do with it and what color you want. That’s very popular in the upper end of the client market,” says Thomas, owner of Diversified Materials & Construction of Missoula and Polson, MT.
But this particular project had many other factors involved as well. The Confederated Salish and Kootenai Tribes, who oversee construction below the high-water mark of Flathead Lake, maintain strict regulations for shoreline protection retaining walls. Thomas did not have many options, as he had to abide by the tribes’ restrictions for permitting. The Tribes’ 64A Shoreline Protection Ordinances recommend wood or riprap walls for the natural look they provide, with concrete walls being used as a last resort.
Additionally, tribal regulations call for wave speed, upon hitting a wall, to be slowed in an effort to prevent erosion and sand transport.
But in Polson, a Flathead Lake resident’s rotting wooden retaining wall on the shoreline of his residence led to the tribes’ considering other alternatives to traditional shoreline protection walls: a Redi-Rock concrete retaining wall.
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