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Retaining Wall and Drainage advice

Posted by bigbigblake TX (My Page) on
Tue, Feb 5, 13 at 14:59

I am building a very small retaining wall in my backyard. We are going to use the Pavestone Windsor Wall at 2 feet tall. I will continue the wall along the back of the house, then around a tree (removing an existing limestone circle). The total length of the wall is about 75 feet.

I am at the point where I am about to buy materials for it and want to run it by someone before purchasing.

The wall bricks are 11 5/8 inches wide. We intend to do a base of around 22 inches wide, 5 extra on each side.

We have a lot of clay in our yard so I intend to put gravel fill behind the wall. For such a short wall I feel like 5 inches should be plenty wide? I also think I will put a slotted drainage pipe with sock behind it to help with water issues.

From what I understand you should put down landscape fabric, lay 2 inches of gravel, lay the drainage pipe, and
then more gravel on top. Then wrap the landscape cloth over the top? Is this correct? Do I also need landscape cloth against the clay where it turns into gravel?

Finally on a 2 foot wall how high do I bring the gravel? Up to the final brick? That would be 4 inches of dirt on top?

Final question, we are wrapping the wall around a tree and removing an existing limestone wall. The existing limestone wall was about the same height and had zero drainage on it. Should I continue the rocks and drainage sock behind the wall where the tree is? My wife seems to think we would want water pooling there for the tree, but I am not sure it was done correctly.

Sorry for the wall of text, but I am getting the last minute jitters before finishing the project.


Follow-Up Postings:

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RE: Retaining Wall and Drainage advice

Here is a image of the circle we are removing on the tree and taking the wall thru this.

On either end of the wall I intend to tie the drainage into our existing drains.

Once the wall is finished I will be removing the patio and all dirt in-between house and the wall and putting pavestones in.


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RE: Retaining Wall and Drainage advice

It would be a lot easier to understand the project if you had pictures that showed the OVERALL project (instead of close-ups.) Since you're tying some new drainage into existing drains, it's not possible to know if this is good without knowing how everything drains and what it's draining. Is there drainage trouble now?

Your overall drain-behind-the wall scheme seems fine, but you don't need to use so much gravel above the pipe. It won't hurt anything, but it's just more work and expense than you need for such a small wall. If you had 3-4" above the pipe, you'd be fine.

"Do I also need landscape cloth against the clay where it turns into gravel?" I do not understand this question.

At the large tree, it sounds like you're removing material and then placing something back. That sounds like it might be the faulty part of this plan. You'd need to show where you're doing what for it to be understood since proximity makes a difference.


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RE: Retaining Wall and Drainage advice

This picture is the original before doing anything. The pink is the basic wall we are trying to build and the yellow spots are existing surface drains that engineer recommended and installed before we moved in. They drain to the street thru the front yard. I planned to tie in the drainage from behind the wall to these drains.

I am removing the limestone/concrete ring that was originally installed around the tree and putting the wall in its place to keep it uniform. The backside of the tree will be brought up to level with the rest of the grass, while the front and sides will be walled.

Regarding the landscape fabric, I really don't understand what all I need to do with it. I know its supposed to wrap the gravel around the drainage pipe, but do I need it anywhere else behind the wall? I guess that is a better question. Should I put it under the base or anything like that?

I am glad you think the gravel is a bit much. The people we are working with wanted me to have 8 inches of gravel behind the wall and up to the very touch. Lowering that cost will help immensely as well.

Don't have any other pictures really so hopefully this helps, if not I can take some more tonight.


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RE: Retaining Wall and Drainage advice

Here is the unedited picture just in case.


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RE: Retaining Wall and Drainage advice

By looking at the new photo, it's not obvious what the grade is doing, but it looks like there are potentially tight and tricky tolerances. Grade is frighteningly close to the lowest siding and it looks as if you may have plans to raise it behind the tree (?)... still not sure exactly what you're doing. But not having the grade right to drain, and expecting to have an underground pipe system carry all the water that might occur in an extreme storm event, seems like it's asking for trouble. Do not understand your pink line and what part of a wall it represents. If I were you, I'd take some grade measurements (with a taught string and line level ... it's cheap and easy) in order to share a reasonably accurate idea of what grade is actually doing. Not trying to be an alarmist, but I have a suspicion that you are getting ready to undertake a project that may not solve your problem, but make things worse. Again, I ask, is there drainage trouble now? (It looks like there is but it would be good if you confirm and explain it.)


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RE: Retaining Wall and Drainage advice

There is only a 2 inch difference between the back of the yard and the spot that I picked for the wall. The pink line will be the location of the 2 feet wall. Currently like you notice the grade is way to close to the siding and the patio is built level with the siding. Once the wall is in, we will be lowering the level of all the dirt to about 5 inches of foundation showing and filling the entire area with pavestone and sloping into the existing drain systems.

The engineer claimed our drainage issues were fixed with the system they installed in place and we do not have any standing water anymore after our 1-2 heavy storms a year.

We are "Mostly" doing this project for appearance reasons more then need, as the dirt backyard is killing us.


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RE: Retaining Wall and Drainage advice

  • Posted by catkim San Diego 10/24 (My Page) on
    Wed, Feb 6, 13 at 15:05

As devil's advocate here -- wouldn't it be cheaper and a far superior result to remove the poorly placed tree and start with a new specimen planted in a more appropriate location? Are you fixing the problem or accommodating the problem? Just asking...


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RE: Retaining Wall and Drainage advice

"The engineer claimed our drainage issues were fixed " That has the ring of "famous last words" to it. It's one thing to accommodate typical, heavy annual rains, but the biggies (20,50 and 100-year rains) can come as a surprise in any year.

The objective of using filter fabric around the gravel encapsulated pipe is to keep dirt out of the gravel. If dirt washes in, the gravel would lose its ability to act as a filter. Then water would be blocked from entering the pipe. The fabric is essentially a filter for the filter. It's not needed for other things behind the wall.


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RE: Retaining Wall and Drainage advice

I've never heard anyone say "yep, this wall failed because it had too much free-draining stone behind it." 3/4" clean is what, $30/ton retail? Cheap insurance. I say go with your original idea of a good-sized drainage chimney with 3-4" soil over top.

As for how to do the fabric, Yard's dead on when he says the goal is keeping soil and fines out of the gravel. The easy way I explain it to homeowners is that you're making a gravel burrito behind the wall. A good one, like a burrito made by a Chipotle employee of the month. Don't let any of the filling escape.


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RE: Retaining Wall and Drainage advice

Cant believe I posted this in Feb. Anyways, This weekend I finally finished the hardscaping with pavers and a wall. I replaced the drainage system completely and got rid of the corrugated pipes and over sized boxes that collected water for mosquito breeding. Replaced it with a S&D pvc pipe system with grates. Installed new gutters and tied into the new drain system as well.

Im still working on the ground, and we will be putting sod in soonish, but the grading directs the water away from our house, and the drains are barely used.

Its been an extremely wet year, so lots of chances to see water behavior.

We tore out a good portion of roots, but the tree seems to be doing good and surviving. Removing it wasn't really an option at this time.

There were a few things I could have done better now that I have learned a thing or two, but for the first time I have ever attempted this solo, I think it turned out pretty good.


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RE: Retaining Wall and Drainage advice

more


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RE: Retaining Wall and Drainage advice

another


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RE: Retaining Wall and Drainage advice

and the last


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RE: Retaining Wall and Drainage advice

Thanks for showing the pictures. The work does look pretty good for a first-timer! It sounds like you've achieved all of your goals, so congratulations on that. I would like to make one suggestion. The work looks clean with one exception and that's how the wall terminates in the first picture, at the far end. The small saw-tooth step-downs look out of place with the rest of the wall's simplicity. It would be better to turn the wall at that point 90* directly toward the back fence, keeping it as a single level (two stones plus cap) so that it matches with your other step-downs. Other than that, it looks fine.

How did you measure for cutting the stones at the wall (first picture)? Looks like it might have been "fun."

This post was edited by Yardvaark on Mon, Jul 29, 13 at 17:39


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RE: Retaining Wall and Drainage advice

That's a good point Yard. Neither my wife nor I are very happy with how the end of it turned out, so I very well might be re-doing it at some point when I'm not so tired.

The cutting of stones was a bit of a learning curve. I ended up redoing quite a few of them my second time round.

I was just manually measuring with a straight edge ruler and getting a little creative with my curves to help lock it in. There were sadly a ton of curves to cut.

We rented the saw the first day late for 24 hours. So I worked from 4pm or so until 8pm on them. By the end it was going much better. Sure enough the next morning I woke up at 7 am to finish up and it was sprinkling. Started cutting in the rain until about 11am when it started pouring. We realized how slow it was going and that I would have to rent the saw again, so my wife convinced me to stop working in the rain and return it. Sure enough as soon as it was back, the rain stopped.

I doubt I would have finished either way though, never expected it to take that long to cut so much. I ended up working a full day from 7am to 8pm to finish the pavestone and capstone.


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RE: Retaining Wall and Drainage advice

Maybe you already know, but in case not, I'll offer one tip that will make cutting easier if you ever do any more pavers in the future. If you measure a uniform paver length distance away from the wall and mark with a yellow crayon, you can mark all the cuts in one operation. After cutting and placing all the cut pavers in place, then just plop in a row of pavers to to finish the area. In the case of pavers with irregular sizes such as you have used, you'd create a uniform band out of the available shapes.


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