5 Reasons Your Retaining Wall Failed

(…and how we can fix it.)

5 Reasons Retaining Wall Fail

This one was unfortunately from just a couple weeks ago, and maybe more unfortunate for the homeowner, was only a week or two old when this happened. The things that went into the failure of this wall are common across nearly all the wall failures we see. And they’re preventable.

Here’s our list of the 5 main (preventable) reasons we see retaining walls fail.

Reason 1: Improper Backfill. There are a few different ways I’ve seen contractors and DIYers alike get this part wrong. Water behind a retaining wall is one of the leading killers, either through the buildup of hydrostatic pressure or freeze-thaw cycles. In the case of hydrostatic pressure-caused failures like the one above, a poor draining, poorly compacted backfill can hold on to large volumes of water after a heavy rain, and when the water doesn’t have an easy way to get out from behind the wall, pressure builds on the wall. If that pressure is more than the wall (as it was constructed) can handle? It’ll blow out like this one did.  These walls need an envelope of clear draining stone that empties into drain pipe that daylights out the face of the wall at regular intervals, so water always has a quick way out.

Reason 2: Improper Block Selection (Know what you’re getting into). There’s nothing wrong with the block in the photo above, when walls are built with it properly. But you have to know going into the build what you can and can’t do with the different block out there. This particular block has a depth of 9″ – again nothing wrong with that, but that makes it a small block to build a big wall from. To do it right there would have to be significant engineering of the soils behind the wall, geogrid, drainage. Second thing about this block is it has a hollow core. Again nothing wrong with that, but this is a gravity wall, so the more mass in the wall, the more earth it can retain. Hollow block means less mass, so there would need to be EVEN MORE steps taken to engineer it properly.

Reason 3: No Embedment. For most 12″ deep, solid retaining wall block, engineered build specs call for embedment of at least 10% of the exposed height of the wall. That means for a wall 48″ high, at least 5″ should be below grade on the face side of the wall. Why does this matter? It connects the wall to the earth, like an NFL lineman’s cleats helping him dig into the earth to resist forces being applied against him. If that same lineman wore dress shoes on the field? He’d get pushed all over.

Reason 4: No geogrid. What’s geogrid? Learn more here. The wall in the above picture was as high as 4′ in some spots, and with a 9″ deep, hollow block, it definitely should have had multiple layers of geogrid, to help recruit the retained soils to the job of retaining themselves. Properly used, geogrid effectively makes a retaining wall many feet thick – pretty tough to knock over a wall that massive!

Reason 5: We didn’t build it. In all seriousness, if you’re building a low, decorative garden wall, you don’t need someone versed in engineered specs for earth retention to build it. Weekend warrior your heart out! But if this is a wall that’ll be 3′ or taller that you need to remain standing for years? Call someone who’s been successfully building these kinds of walls for more than 20 years in the Fox Valley. Call Stonehenge. (920)830-4550.

And if your wall is already built but looks like it’s on it’s way to looking like the one at the top of this page?  Give us a call – there’s not a retaining wall out there we can’t fix.

Additional resources from Stonehenge:

Retaining wall rebuild
Retaining Wall Disaster (Thankfully nobody was injured)

Now here’s a gravity wall (big boulders in the north woods)
20+ year old retaining wall