If you’ve spent any amount of time driving around the Fox Cities, you’ve probably seen a few retaining walls toppled over, or at least leaning pretty hard in the wrong direction. There’s a business on Bell St in Neenah (I won’t say any names but it’s near highway 41) that upon driving by it years ago for the first time on a client appointment, I noticed this beautiful snap-faced limestone wall had a lean to it.
I climbed out of my truck, took a few quick pictures, and later that week sent a letter with pictures to the business explaining that I was worried about their beautiful wall falling over (a wall we hadn’t built), and that I could fix their wall so it didn’t collapse on them.
I never heard back, and a couple years later my fears were realized when I saw a good portion of the retaining wall spilled out onto the ground in front of where it used to stand, like Legos thrown to the ground. The business opted for a quick fix, simply re-stacking the stones, and several years later, the wall again, like a drunken bar patron set on making it to last call, had fallen over.
There are really only two or three reasons why retaining walls fail. One of the most common is inadequate drainage behind a wall. This lets the freeze-thaw cycles like those that are about to be a daily occurrence in Wisconsin in March and April (and again in October and November) push on our clay-backfilled retaining walls by night, the ice melting and working deeper by day to push again the following night.
But another very important reason that retaining walls in Wisconsin’s Fox River Valley fail is that the walls are being asked to hold back more earth than they are capable of retaining. Well-meaning do-it-yourselfers and even landscape contractors who should know better are building retaining walls that are destined for failure. They’re being built higher than can be sustained without reinforcement, and it’s leading to clients in our area having to spend tens of thousands (and one client I met was faced with the prospect of having to RE-spend hundreds of thousands) of dollars having these retaining walls torn down to the ground and rebuilt from scratch. Don’t believe us? Go ahead and Google retaining wall failures and see what you find. The project pictured at right is local, right here in the Fox Cities. It was not built by us, and this image shows only a portion of the multiple, catastrophic failures. Our post-failure inspection found virtually no reinforcements.
How a Retaining Wall Is Reinforced
The way a segmental retaining wall is reinforced is straightforward and the materials required aren’t that costly. It requires more digging and more subsequent backfilling and compaction, but that cost is tiny compared to the cost of paying twice to have a retaining wall built. (As an aside, sadly many clients’ eye on strict bottom-line numbers don’t know to ask about geogrid or if it’s needed on their project, and will end up choosing a contractor who just doesn’t understand the mechanics of a retaining wall or when geogrid is needed, and the money they save today ends up costing them down the road. We’re not just spouting “you get what you pay for” platitudes here. We’ve been on countless appointments where a lawsuit is pending, where the prospective client is suing their previous landscape contractor for faulty workmanship, and they’re trying to figure out how much to sue for in court.)
The material used is call geogrid. There are several manufacturers and a few different styles, but geogrid of all types is best described as a woven fabric of high tensile strength that is pinned between layers of retaining wall and extends back into the soils the wall is retaining, to lock together the block or stone wall with the soils behind it. Adding geogrid to a retaining wall recruits the retained soils as helpers in retention, essentially making the retaining wall far more massive than the weight of the block or stone alone.
When Is Geogrid Needed in a Retaining Wall
When grid is needed depends on the wall building material but also the soils being retained. Clay soils, which are ubiquitous throughout Appleton, Neenah and all of the Fox Cities, are the most cantankerous, least cooperative soils in existence. They resist compaction. They hold onto moisture. They swell when moist and contract when dry. They are the worst soils there are to work with, and the hardest to retain. The material chosen for the retaining wall matters, too: the more massive the material being used, the less geogrid is needed. For most 6″ or 8″ wide split-face limestone retaining walls, geogrid will be something to consider when the exposed wall height exceeds 24″. For most man-made retaining wall block, geogrid becomes desired at exposed wall heights of 36″-48″, depending on the block design (and size), whether there’s a surcharge at the top of the wall, if there’s a slope at the base of the wall, as well as a few other considerations. Once the retaining wall is over 6′ in height, if it isn’t being built from 24″+ wide limestone outcroppings or similarly sized, dense material, geogrid is required.
At Stonehenge we keep abreast of industry news and up to date on technical specifications of the retaining wall blocks available to us for constructing retaining walls. And we back our knowledge and experience with an industry-best guarantee.
"With Stonehenge you get a company that's rich in experience and large enough to tackle any project you could possibly throw at us, but small enough that you'll see the same faces throughout your entire experience. " - Jeff Pozniak, President
