Retaining walls are among the high challenge, high reward side of garden landscape improvements. They feature many of the difficulties in creating free-standing walls, with the added challenge of holding back a great weight of soil and water.
Retaining walls done in series up and down the elevation of a landscape are called terraces. These are highly labor, material, and time intensive projects. But the payoff is level ground where a hill once stood!
As you are planning the location for the location for the installation, it’s important to notice the water and weather of the area. Your retaining wall is going to come into contact with any groundwater moving thru this area. So, while old railroad ties are often used, we here at Sustainable Landscape Services do NOT recommend these materials. They may have sustainable value as salvage, but their creosote-laden timbers are not for us!
Everyone’s seen and knows about pre-cast, segmented unit walls, so what’s the fun in talking about them? Moving on!
Gabions are really neat. They’re like a wonton, where the wrapping is made of chain-link fence and the stuffing is made of large, rough rock. They’re a great option if you can use a lot of local rock. They also provide a quick, extensive border. Their high permeability also makes them great for controlling water across a landscape–they slow but do not stop water movement.
No matter what you choose to construct, you’ve always, always got to account for hydrostatic pressure. In short, all the water in the soil above and behind a wall is being pulled by gravity. The water wants to run downward, yes, but it also flows outward. This force can build to tremendous levels across lengthy walls. Always be sure to include behind-the-wall drainage, and weepholes if you want.
Another way to address this pressure is to anchor the wall back into the hill behind it. You can do this thru traditional means, like using ‘deadmen’: posts going perpendicular to the wall and driven down into the earth as a great stake. But a somewhat new technology–with ever-newer materials–is something called a geogrid. It’s basically a layer placed while building the wall and buried into the hillside.