Geogrids Make Retaining Walls Stronger

From the www.homefocus.com website.

If you're thinking about building a landscape retaining wall, there's something new out there that can make your installation more reliable. It's generically called ''geogrid'' -- a synthetic textile mesh that stabilizes soil, boosting the success rate of all but the smallest retaining walls. Although you won't yet find geogrid products at retail-level outlets, it's worth pursuing from industrial suppliers. Even if you're hiring someone else to build your retaining wall, don't assume that geogrids will always be installed where they could provide benefit. If you run into a landscape contractor who doesn't know what geogrids are, pick up the phone and find another.

Traditionally, the only thing that kept retaining walls standing was the mass of the wall itself, and the degree that the wall sloped into the soil being retained. Although these two factors can sometimes be enough to endow a retaining wall with a long and non-eventful life, they're often not sufficient. That's why it's so common to see retaining walls losing the battle of the bulge; leaning, breaking and flopping over as a result. Why risk this outcome when you don't have to?

In the early 1980s, geogrid technology made its way across the Atlantic from England. The photo of the installation-in-progress shows how it's incorporated into the backfill held behind a retaining wall, and woven into the masonry units making up the structure. This endows the soil mass with enough internal strength to resist the forces of gravity pulling it downhill. Geogrid does for soil what steel reinforcing rod does for concrete. It adds tensile strength to a material that would otherwise only have significant strength in compression. It's been used to support retaining walls and steep slopes along highways and on numerous rail embankments.

Depending on the situation, geogrid is installed in horizontal layers, with varying spaces and embedment lengths, depending on conditions. It's presence takes sideways pressure off the wall by transforming the soil into a structural part of the system, not just a load to be held back. In fact, it's even possible to build a masonry-free retaining wall, using only geogrids to stabilize the soil, while vegetation-covered landscape fabric forms the visible face. Imagine a flat, green, steeply sloping face and you'll get the picture.

Regardless of design, geogrids are easy to apply, invisible in the finished installation, and an inexpensive way to ensure long-lasting, trouble-free retaining wall performance. Cost is about 0.50 cents per square foot for residential-grade versions.

Some geogrids look enough like plastic snow fence that some people try to save money by substituting, though that's bad idea. All brands of geogrid are engineered products, both in terms of manufacture and installation. Most types are designed to minimize the stretch-factor of the product along its bearing axis (the woven strands), but with little lateral strength because none is required. This is called uniaxial geogrid. The slightly curved fibers that extend from left to right are just for connecting to the wider, woven strips -- the ones that actually do the work. Geogrids that are strong in all directions -- called biaxial -- can be used to strengthen road and driveway surfaces, too, preventing tire track rutting. Permanent roads have even been built over peat bogs using biaxial geogrids.