If youve spent any amount of time driving around the Fox Cities, youve probably seen a few retaining walls toppled over, or at least leaning pretty hard in the wrong direction. Theres a business on Bell St in Neenah (I wont say any names but its 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 hadnt built), and that I could fix their wall so it didnt 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 Wisconsins 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. Theyre being built higher than can be sustained without reinforcement, and its 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. Dont 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 arent 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 dont know to ask about geogrid or if its needed on their project, and will end up choosing a contractor who just doesnt 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. Were not just spouting you get what you pay for platitudes here. Weve been on countless appointments where a lawsuit is pending, where the prospective client is suing their previous landscape contractor for faulty workmanship, and theyre 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 theres a surcharge at the top of the wall, if theres 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 isnt 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.
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Are you wanting to know more about geogrid in hardscape? If you are preparing to install pavers in your yard, youve likely been advised to implement geogrid in whatever hardscape you install. But when should you use geogrid? What is its purpose? How long does geogrid last?
In this blog post, well answer the most frequently asked questions about geogrid so that you can be equipped with knowledge before you begin your hardscape project.
Geogrid is used in almost every type of hardscapefrom driveways to walkways to patios and everything in between. However, it is essential in retaining walls, particularly those above three or four feet.
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Pro Tip
Geogrid should be implemented whenever you want your hardscape to last and stay structurally sound.
It is better to install geogrid and learn later that it might not have been necessary than to skip using it and have your wall crumble a few years later.
Geogrid is used in slope stabilization, soil stabilization, and soil reinforcement. Geogrid is crucial in keeping your hardscape interlocked while the environment around it naturally swells, shrinks, and shifts in response to climate and seasonal changes.
Yes, it is ideal to use geogrid in all retaining applications. For most man-made retaining wall blocks, geogrid is desired at 36-48 exposed wall heights.
If steep slopes are near the wall, loading above the barrier, tiered walls, or poor soil, geogrid becomes even more necessary, regardless of wall height.
Products such as a weed barrier or orange safety fencing are not the same thing as geogrid. Geogrid is intentionally designed with specific ribs and patterns to minimize shifting and settling.
Pro Tip
The cost of implementing geogrid in your initial installation is well worth the alternative of rebuilding your hardscape after only a few years.
Woven textiles can provide a highly efficient and cost-effective alternative to rigid polypropylene geogrids for base stabilization applications. However, if the instructions for your retaining wall block tell you to use geogrid do use geogrid.
Your geogrid will essentially last forever.
Tests have shown that geogrid has virtually no degradation for exposure in an outdoor environment for 12 months. This means that degradation will not happen even if geogrid is left exposed to the elements.
There is even less chance of degradation when geogrid is underground in a dense aggregate environment, as it usually is. Your geogrid will last as long as your hardscapelikely longer than you!
Yes, you can and probably should. Geogrid reinforcement can be used in thin Portland cement concrete (PCC) members and overlays in pavements and other structures where steel reinforcement cannot be set due to constructability and strength impediments.
Incorporating geogrids into the roadway section effectively creates a stiffer, more uniform foundation that will maintain well and for a long time. You can read more in this article where the Arizona Department of Transportation describes how it used geogrid in the paving of US 89T.
If you use geogrid, you can reduce the depth of excavation required on unsuitable subgrades. This means less digging and excavation, making your project more straightforward.
Geogrid does wonders to strengthen the soil and provide enhanced safety and excellent seismic durability by stabilizing slopes. Geogrid ensures that your retaining wall wont fall over!
Another advantage of geogrid is that it reduces differential settlement. Geogrids lessen the need for maintenance and extend the lifetime of paths, roads, walls, and more.
Geogrids have higher tensile strength than the soils they contain and, depending on their size, can endure heavy loads. With a tensile strength of lbs/sq ft, geogrid can easily withstand heavy vehicular traffic (even trucks carrying heavy loads), aid in retaining solid walls and steep driveways, and hold up under an extremely high volume of foot traffic.
Geogrid is placed atop the subgrade (the primary layer of earth below your project) and below the AB (aggregate base). In other words, dirt, sand, or large rock should be below the geogrid and ¾-0 road base gravel installed on top of it.
Geotextiles are for separation, filtration, and drainage purposes, while geogrids are used specifically for reinforcement. If you want to build a strong hardscape, use geogrid.
If you need guidance for installing your hardscape (and geogrid), download our free Project Planning Guide.
If you want to learn more, please visit our website Geogrid Supplier.