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rjschwar 11-13-2009 11:57 AM

Retaining Wall and Muddy Yard
This is kind of a two part question. My wife and I purchased a house and end of the back yard sloped down into our neighbors yard, down about 10 feet, out about 20. We had someone come in and install two terraced retaining walls and regained about 10 feet of yard. We used ecology blocks (2'x2'x6' concrete blocks w/ a rebar "handle") for the wall. The upper wall consists of 3 blocks of which one is completely buried leaving 4' above ground. They also leveled our yard (it was always fairly flat, but there was one section that quickly dropped off a few inches creating a, so a portion was lower than the other part of the yard), and graded it away from the house, and brought in several layers of top soil. We had no problems with mud or drainage before this happened, however now we have had alot of rain in the last several weeks, and our yard if very muddy. There was grass/weeds when we started, but now the flatter yard is just dirt, and we were going to replant grass in the spring. As I said, there was no water issues before, but now the yard is muddy. If you walk on it, you sink several inches, and your boots tend to stick into the ground. My first question is will this likely be alleviated when we plant grass, as the grass will be absorbing the moisture, or should the yard be graded more than it is? As I said, it currently gently slopes away from the house, and the foundation stays dry, so no basement issues, just the yard being wet. Secondly, when they installed the retaining wall, they only put a drain tile (drainage rock and a pipe) near the bottom of the wall. The put no drain rock between the wall and fill. The wall has begun to lean, and they are returning to fix this. My question is how is the best way to do this? I was going to have them add drain rock up the entire face of the rear of the wall to allow water to drain, and also slightly slope the blocks into the hill. Will this be adequate? I am not sure if the drain rock behind the wall will work because the yard retains so much water currently. I have read about hydrostatic pressure, but is this caused from the water itself actually pressing against the wall, or from water saturated soil gaining mass, and putting more force against the wall? If the water is creating the force, the drain rock would seem to solve the problem, as it would all just drain away, but if it is just soil that retains water, I don't know how much the drain rock would help. Finally what is the ideal grade for a yard to facilitate drainage, but still be "flat" for usability? My yard is about 35' long, by 50' wide (50' retaining wall). Also, with the drain rock behind the wall, should the yard slope completely away from the house, w/ the highest part being the foundation, and the lowest part being the retaining wall, or will this cause retaining wall issues (it seems to me even if the wall is the lowest part, the drain rock behind it would create a place for all the water to go away to)? The other option would be to have the retaining wall and foundation both higher, creating a slight V shape in the middle of the yard, and drain off to the side. I'm not sure of the type of soil that I have, but I previously figured it had pretty good drainage because the yard never had water problems before, now I'm not so sure. Any input would be appreciated. Sorry for the long post all in one paragraph, but whenever I saved my changes, I couldn't add any white spaces. Thanks, Richard

drewguy 12-15-2009 12:02 PM

If the wall is leaning, you definitely want to get them back there. It may be that they didn't create enough drainage through the walls.

As for the muddy, sinking feeling, was the fill mostly topsoil? That absorbs more than a clay subsoil and probably was not compacted. That's part of the reason you were sinking in. You may want to roll it before planting grass in order to get it packed down more.

Bondo 12-17-2009 06:19 PM

Ayuh,... I've tried to read that Twice,.... I think I deciphered it...
Ever heard of a Paragraph,..??

Who designed the project,..?? You or the Contractor,..??

We used ecology blocks (2'x2'x6' concrete blocks w/ a rebar "handle&quot
What does That mean,..??

but now the yard is muddy.
That's what fresh Dirt is supposed to be like,.... Yes, grass,+ weeds is Better but takes time...

That's why I asked Who designed it, it sounds about Right as it is....
As to why it's leaning, I can only assume that portion might have been build on a fill, rather than on a fresh cut....
If the Contractor designed it, let him do his job, it sounds like he's got a handle on it....

rjschwar 12-18-2009 10:36 AM

The contractor designed it, but didn't put much drainage behind it. My description of the ecology block was for people who might not be familiar with them. They are basic 2x2x6' concrete blocks w/ a piece of rebar embedded in the top so that they can be lifted (with machines obviously).

The contractor has since returned and taken down the wall. He is coming this weekend to rebuild it. The plan is to add 12" of drainage rock, and slope the wall slightly back into the hill.

You are correct, the upper wall was a back filled wall. The lower was cut into the hill. The lower wall is leaning slightly as well, but it seems to be leaning because the top was leaning, and this forced the lower one to move slightly. There is drainage below the lower wall, but not behind. As it was cut into the hill, I don't think this wall is in much risk of toppling, but it is defiantly leaning slightly. Will the lower wall be OK without drainage behind it since it was cut into already settled dirt?

The mud has gotten better. I was concerned that maybe there wasn't enough sloping in the yard, but we had record rainfall right after the wall was built, and the dirt hadn't had time to settle.

Sorry about the previous post. Yes, I have indeed heard of paragraphs, however at the time whenever I added a newline, when I posted, all white space was removed. It took me a while to find the settings in User CP to change the editor formatting. Luckily now I am able to separate my posts instead of posting something that looks like the first sentence of A Tale of Two Cities.

Bondo 12-18-2009 01:03 PM


The contractor has since returned and taken down the wall. He is coming this weekend to rebuild it. The plan is to add 12" of drainage rock, and slope the wall slightly back into the hill.
Ayuh,... From what I could read in your 1st post, I don't really think you're lacking drainage, If the drainage itself can drain....

I'm also not familiar with your wall system,...
From your description,... It Sounds like it's seriously lacking any Tie-Backs in it...

Regardless of what a retaining wall is built from, it needs mechanical Tie-Backs to hold the weight behind it from toppling it...
If it were mine, I'd want to see Tie-Backs about a Foot below grade, maybe 18" deep...
Going back under the hill by the height of the wall's face, above grade...
And, probably 5 or 6 of them on a 50' span...

rjschwar 12-18-2009 01:34 PM

This is a gravity wall. There are no tiebacks. I know people build gravity block walls w/o tiebacks or geogrid w/ things like keystone blocks, but these ecology blocks are bigger and cheaper. Each of these blocks weights something like 3000 lbs.

That is an example of what I am talking about.

Daniel Holzman 12-18-2009 03:05 PM

This is indeed a gravity wall, hence if properly designed does not need tiebacks, unlike a reinforced earth wall, which does need tiebacks.

As for the leaning, it is possible that the wall leaned (I assume in the outward direction) due to hydrostatic pressure caused by lack of drainage on the uphill face of the wall. With a few very unusual exceptions, gravity walls require a draining blanket, usually composed of crushed stone, on the entire upstream face of the wall. This is to allow water to drain downwards, where it is usually captured by a drain tile near the footing of the wall, and directed away from the wall. Alternatively, you can install weep holes in the wall near the bottom to allow drainage through the wall.

Failure to provide adequate drainage can result in water pressure on the upstream face of the wall sufficient to cause the wall to either slide downhill or tilt. You may have this condition here, in which case the designer of the wall (the builder) should fix it at no charge. If the wall contractor is unfamiliar with proper design of the wall, they should hire an engineer to prepare plans and specs for the wall, which they can then follow.

rjschwar 12-18-2009 03:17 PM

He has indeed agreed to fix it at no cost, and is adding drainage the full length of the wall 12" wide (to the upper wall). There is already drainage at the bottom (pipe in gravel taking water to edge of wall and emptying out of a gap in the wall). I agree that the hydrostatic pressure was what was causing the issue, and I think the drainage rock should fix this; we had record rainfall literally the week after this was done, and that is saying alot for Seattle. In addition, he is going to lean the wall a few degrees against the fill. Do you think he needs to dig up the lower wall and add drainage there too? As I said, the lower wall was a cut wall that was cut into well compacted, settled dirt and has compacted minus and drainage at the bottom (maybe lower 1', but the rest of the exposed 2-3 feet of the wall has no drainage rock between the soil and the wall.)



Daniel Holzman 12-18-2009 03:32 PM

The lower wall should have drainage behind the wall as well, however as it is only three feet tall it is not as much of a problem. However, should have been there in the first place, so if the contractor is going to repair the upper wall, perhaps they will repair the lower wall as well.

rjschwar 12-18-2009 03:40 PM

Thanks, I'll talk to him about it.


rjschwar 02-24-2010 12:55 PM

Well, once the top leaning wall was taken down, the real cause showed up. The dirt below the wall was not as solid as it should have been. Although the contractor put down i think 6"-1' of crushed beneath the wall, parts still sank, and that is what caused the leaning.

I would make sure the "foundation" dirt is solid, and have alot of crushed rock put down under the wall, especially the higher tier. Obviously drainage is important as well, and we had him put about 1' of drain rock behind the walls, and connected pipes at the base to collect and divert all the water.

You may also want to lean the ecology blocks into the hill slightly. Ours aren't really leaning, and it hasn't appeared to have moved at all yet we have had some rain. It appears to be solid thanks to more drainage, and a better foundation.

Also, make sure at least half maybe the full lower tier blocks are buried (below grade) before you start building up to help with the foundation.

One idea to make up some of the height would be to slope the terrace a bit, you could gain half a foot to a foot this way. We are planning to just plant trees there anyway, so that is what we did.

Finally, make sure your top wall is far enough away from the bottom wall to be independent. Check w/ local codes etc.

We have yet to build a fence, but are planning to bolt it right to the top of the ecology blocks. We didn't put any top soil on top of the drainage rock or the ecology blocks, but may just add a bit more drainage rock on top of the ecology blocks to make a nice divider between grass and fence. Beauty bark is another possibility. You might also be able to find an ecology block cap which makes the top of the ecology block look kind of like a sidewalk. They are same length and width of blocks, about 1' high, and completely flat on top. Nowhere around here had them, but I have seen them before.

Let me know if you have any other questions.

Good Luck,


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