This incident happened only a week or two ago, which is much worse for the homeowner than it is for the homeowner. Nearly all of the wall failures we observe share the factors that led to this wall’s downfall. And they may be avoided.
Here is our list of the top 5 (preventable) causes of retaining wall failure that we observe.
Reason 1: Improper Backfill.
Contractors and do-it-yourselfers alike have gotten this portion incorrect in a few different ways, in my experience. One of the main causes of death is water behind a retaining wall, either because of the development of hydrostatic pressure or freeze-thaw cycles. A poor draining, badly compacted backfill can retain significant amounts of water after a heavy rain, and when the water doesn’t have a simple path to escape from behind the wall, pressure accumulates on the wall, as in the case of hydrostatic pressure-caused failures like the one above. If the wall (as it was built) cannot withstand the pressure? Like this one did, it’ll blow out. For water to constantly have a speedy exit, these walls require an envelope of clear draining stone that empties into a drain pipe and daylights out the face of the wall at regular intervals.
Reason 2: Inappropriate Block Selection (Be Prepared).
When walls are constructed properly using the block in the picture above, there is nothing wrong with it. However, you must be aware of what you can and cannot accomplish with the various blocks available before beginning the project. This particular block has a depth of 9′′, which is fine, but makes it a little block to use for a large wall. For it to be done properly, the soils beneath the wall, geogrid, and drainage would need to be heavily engineered. The block’s hollow core is the second feature. Again, there is nothing wrong with it, but because this wall is supported by gravity, the more mass it has, the more earth it can hold. Hollow blocks have less mass, therefore good engineering would necessitate even more effort.
Also Read: Three typical mechanisms for geomembrane failure
Reason 3: No embedding.
Engineered build specifications call for the embedment of at least 10% of the exposed height of the wall for the majority of 12′′ deep, solid retaining wall blocks. This indicates that on the facing side of a wall 48 inches high, there should be at least 5 inches below grade. Why is this important? It links the wall to the ground, similar to how an NFL lineman’s cleats enable him to dig into the ground to fend off forces being applied to him. Suppose that lineman still played the field with dress shoes? He would continually be pressed.
Reason 4: There is no geogrid.
Describe geogrids. Find out more here.
The wall in the above image was as high as 4 feet in some places, and with hollow blocks that were 9 inches deep, it most definitely needed numerous layers of geogrid to encourage the retained soils to do their own self-retention. When used properly, geogrid forms retaining wall designs many feet thick, making them very difficult to topple.
Also read: Rail Infrastructure Resilience Starts with A Geogrid-Stabilized Track
Reason 5: We didn’t construct it.
In all seriousness, you don’t need an expert in designed specifications for soil retention to build a simple, attractive garden wall. Weekend warrior, go for broke! But what if this wall is 3 feet or taller and you need to stand there for years? Looking for a geogrid retaining wall designs? Call +91 9090919019 or enquire at enquiry@singhalglobla.com for more information. We offer a variety of geogrid retaining wall solutions to meet your needs.
