How to fix/repair retaining wall?

[mrblotto]

Hey everyone,
Back when we first bought our home ('97), we installed/put up a retaining wall between our yard and the neighbors, as there was a pretty big slope between us. Everything would basically wash downhill to us

Anyhow,
Everything has been great, except we're now noticing that the retaining wall appears to be sliding 'back', like dirt/earth has been removed and it's falling back on itself. Here are a couple pics for reference.

See how it's falling/leaning 'back'? We're trying to figure out the best way to level it back up.

-take off the top 4 or 5 levels, straighten them up, and backfill?
-start from one end to the other? (like left to right?)
-stick a big ole' metal rod/tamper down behind the wall and push it forward, then backfill?
-what to backfill with - rock/gravel (my choice), or dirt?

I'm thinking we'll have to curve the wall around some more in the 2nd pic, to kinda 'cut off' the slope so stuff wont wash out so much

Any ideas are appreciated
Blah-Toe

 

[NutBucket]

Be happy it's going backward not forward. Furthermore, be happy that it's failure wouldn't ruin your house (at least from what it looks like).

I'm trying to figure out how it is leaning backwards. Maybe the footing heaved due to frost? It's about the only explanation I can come up with.

 

[momeNt]

You "think" it's leaning backwards. The load on the wall is greatest against the bottom, the bottom of the wall is probably actually moving forward. The reason you see retaining walls leaning forward, is because the base is fixed, and the top of the wall is failing, in your case, your base is loose, and is failing against the load at the bottom.

Bigger the arrow the bigger the load.

The bottom of your wall is failed. I think your best course of action is to probably take the whole thing down, and use an anchoring or tieback system to anchor the wall.

You can actually use the earth itself to anchor the wall. There are mesh panels that you can secure to the wall, that will stretch back onto the backfilled area, that creates a tieback of sorts where the weight of the soil on the grid holds the wall in place.

http://www.rhizomebarrier.com/copy-of-dupont-gravel-grid-4-x-25-50-mm-x-55-mm-cell-size-1/

 

[Dranoche]

Most likely settlement of the fill materials directly behind the block. Nothing to indicate other failure modes, plus no reinforced mass behind the block to make most them feasible. Failures to cause that rotation would have other signs like bulging in front of the wall, plus the tree still looks to be fine. I would be concerned about the tree though; is it on top of the wall or was the wall built around it? How tall is the wall, 24-30" maybe? Minor landscaping wall, but no matter how short, I might be concerned about a tree sitting on top of it near my driveway.

Best thing to do would be to tear it down and rebuild it, and get rid of the tree. Probably have to replant everything above the wall, but maybe not. Might be able to just re-stack the block if the cut remains standing. Line the face of the soil with a non-woven drainage fabric, re-stack the block, backfill with clean gravel. Place a perforated HDPE drain pipe in the bottom, daylight it at the low end of the wall, and halfway along the length if the wall is more than about 50 or 60 feet. Wrap the fabric over the top of the clean stone so you can finish backfilling with topsoil behind the top couple block courses. Put a small swale or some type of drain on the other side of the landscaped area to intercept water and carry it to the ends, rather than letting it come over the wall.

Can't tell how steep the slope above the wall is but I'm guessing it's not that steep, and the wall is extremely short, so grid shouldn't be necessary. This is a landscaping/maintenance issue. You can wrap the wall further around the ends to hold that material, just make sure you maintain drainage away from the wall. Retaining walls are for grade control, not drainage.

 

[momeNt]

I don't think settlement of the fill materials behind the wall would cause the wall to lean. The wall isn't exerting a lateral force into the fill material.

The wall has probably reached equilibrium over this amount of time though, you maybe only now have noticed it for one reason or another.

Maybe try driving a stake, like a piece of rebar, in the ground in a couple of spots, taking measurements off the stakes to the wall, and check again next year. That'll tell you what is going on.

 

[Dranoche]

The fill material can settle under it's own weight, then you end up with loss of support or a void directly under the back of block. Also could be loss of material over time, washed out by water. It's a really short landscaping wall, so the material behind it probably wasn't well compacted directly behind the block, plus the wall was built to control drainage, so water moving along the back of the block is likely.

A bearing capacity failure or a global stability failure could cause that kind of rotation, but there's no bulging in front of the wall, and the tree doesn't appear to be affected. A very steep slope could cause that in this short of the wall, but it's only a 2-ft tall wall and the slope doesn't appear that steep. A shear failure could cause lower blocks to punch out, but again it's a 2-ft tall wall, the load for that likely isn't there, and that typically shows up as a general bulge rather than an obvious punch-out. A sliding failure can't really occur without a reinforced mass behind the block, would likely show up as local overturning failures instead. Minor washouts during construction of MSE walls often result in the block leaning back into the newly formed void due to the batter of the wall and the loss of support directly behind the block.

 

[mrblotto]

Ouch,
My head hurts from all the complex terms lol. Thank you ALL for the valuable info. First thing I'm gonna do is trim the hell outa those bushes, and finally cut down the tree (or have it cut down). - the driveway is only 4" so perhaps the tree falling on it would crack the hell out of it.

Onward and upward. Thank you all again *salute*

 

[Gardener]

The big tell is the tree, there is no visible root flare. My guess is that 3-4 feet of the trunk is buried in the wall, which is terrible for the tree. The wall was built with inadequate backfill and compaction, there is no indication of any other movement.

Rebuild that wall, Mr. Gorbachev! Leave the tree out of it, curve the wall behind it.