Form & function
1 Jun, 2008 By: Ken Krizner Landscape ManagementRetaining walls combine practicality with design to make properties more useful.
 Well-designed retaining walls work and look great. |
Function remains the most-important element because retaining walls are built to stabilize the terrain or prevent erosion. But these walls can be aesthetically pleasing, as well, because of the many different looks available.
In residential settings, retaining walls can be used for a number of purposes, including leveling a yard or creating a raised patio. In commercial settings, they can be used to level large tracts of land to prepare them for construction projects.
Retaining walls play a role in the visual effect of landscapes. They can be informal shapes or include irregular placement of materials — smaller in size but more pronounced in visual character than more-functional retaining walls, says Michael O'Connell, president of O'Connell Landscape, a design/build landscape contractor in San Rafael, CA. The structures also can complement other landscape elements, such as plants, paving and mulches.
There are numerous types of retaining walls, including poured concrete, conventional stacked blocks and stackable decorative blocks that need no mortar. Manufactured blocks and glass/concrete facade elements are available in a variety of colors and textures and are made to resemble practically any element, from wood to stacked slate, O'Connell points out.
 While "support and separation" is Priority No. 1 for retaining walls, they also should enhance the landscape. |
Site preparation
Many factors should be considered before construction of a retaining wall begins.
"It always starts with how the space is going to be used," says Andy Vande Hey, president of The Vande Hey Co., a professional landscape firm in Appleton, WI.
Other factors to consider are: the overall height of the wall; slopes at the top and/or bottom of the wall, which will change the way the wall is constructed; and whether the wall will be under a driveway, pool, shed or other variable that will put great pressure on it.
"These factors will determine how to build the wall functionally to survive long-term," says Tim Huinker, construction specialist for Anchor Wall Systems, a developer of retaining wall systems in Minnetonka, MN.
When preparing the site, the area should be clear of vegetation, especially above the wall. Site preparation also can depend on the engineering cross-section of the wall, Vande Hey adds.
"If it's more of a structural wall, there will be more preparation involved," he says.
Construction involves digging a footing trench about 12 in. deep and laying in a gravel leveling pad until about 6 in. deep. The wall will lie on top of the pad.
Site access
Access is probably the biggest challenge to building a retaining wall. These walls require different backfill materials and a lot of block. There is likely to be a great deal of excavation work beforehand.
To be as efficient as possible, there is a lot of equipment used to build retaining walls.
"It's nice to have equipment accessibility, but that is not practical at every site," O'Connell says.
Weather can be another challenge, Huinker says, as can be the availability of labor to build the wall.
It's also important to remember the engineering behind a retaining wall. It can take almost no time at all to discover whether a wall is improperly built.
"And the cost to replace a retaining wall is enormous," Huinker adds.
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