Concrete Block retaining wall

19 years ago

I'm got a slope in my front yard that I want to remove by putting in a four foot high retaining wall. I'm planning on building the wall out of concrete block and covering the face with a stone facade that matches the front on my home. The wall is going to be about 90 feet long, running from the end of my driveway across the front of the house. I'm going to put in a PVC drainage pipe behind the wall and fill it up with rock to help move the water away from the driveway and towards the side lawn.

My question is this. I know that I must put in a poured concrete foundation, but how thick should it be and how wide?

Thanks

Comments (5)

pls8xx
19 years ago
tabber,
You may not be getting a response to your question because it is a little more complicated than a simple ratio that would require a certain footer for a given height. A demo program I downloaded from Retain Pro was helpful to me to assess the walls I'm building.

I live in Arkansas and around here there have been a lot of DIY block walls built. Most of them have failed or are in the process of failing. Best I can tell, those that stood up over the years were built on a substantial footer and the block cavities have rebar and concrete. Steel stubs up from the footing to lock the wall to it in many of the block cavities. The good walls that are over 3 feet high were made with 12" block and they all have a system to prevent the ground behind the wall from becoming saturated with water. Not a cheap thing to construct.

Lately, a lot of homeowners have built walls using the modular blocks that lock together. Close attention to the details will bring most DIY walls of this type to a good result. But they are what they are. If you like the look, it's not a bad way to go. If you want a true vertical wall that can have a finish of stone , tile, or some other material, then you have to look elsewhere.

Timber walls are another possibility that some choose. But they aren't a permanent solution. The life span of a timber wall is also shortened if you have a long season where the ground is warm and you garden on the up side keeping the ground wet and fertilized.

In the end I chose to do poured concrete walls. Most would say that this type wall is beyond a DIY project, but in my second year of wall building, I would say that there are no special skills needed, nor is the cost of tools that much more than needed for other types. One might call it an advanced DIY project, not for a beginner. I didn't have experience with concrete when I started but I did have a lot of DIY projects and was well experienced in working with wood. Most would do well to keep their wall heights to 3 feet and under.

Keep in mind that down here the ground does not freeze more than a few inches deep, something that might be a major problem for those in colder areas.

I now have about 200 feet of wall up with another 125 to go. One of the things I like about poured concrete is that I don't have a lot of really heavy lifting to do. There is a lot of labor, but the form panels and other materials are not much more than 20 pounds, something an older man can handle.

James
dorlando
18 years ago
I think I just sent you a separate email but if you could reply to the post instead to continue the thread. how far apart are you putting your vertical rebar in your wall?
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Look at multi-flow drainage systems on google. You need drainage. It probably should have had a wider footing going back toward the slope (called a cantilever wall - the backfill sits on the footing like a fat guy on a chair so that the back of the char can't tip over). He built what is called a "gravity wall" which relies on the mass of the wall being greater than the force of what is being retained so that it won't move. Any water build up behind that wall causes what is known as hydrostatic pressure which adds to the force being applied to that wall. Weep holes would have been a good idea during construction. Now it is a bit more difficult to make the weep holes. At minimum, put in drain pipe and clear drainage stone behind the wall so that the water can get out. What was built is a typical basement wall built to support something on top of it and with a structure holding the top of the walls apart and a concrete slab holding the bottom of the walls apart. He is essentially asking a vertical slab to hold back 40" of fill without pushing out or toppling over.
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Let me start by telling you that you have a beautiful garden! I brought in the expert to look at your question and offer an opinion, the hubby is a bricklayer and has plenty of experience with retaining walls. You, unfortunately, have way too much soil that needs to be held back to prevent the wash out that will occur without a full retaining wall. The terraces would erode rather quickly if you just had retaining blocks stacked loosely. Their strength is in having them stacked tightly with the gravel interlocking them. Sorry to disappoint. Good Luck, Tracy & Ed
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You have been given so many really great suggestions that I don't think I could think of any that are better or more helpful. I did however want to address the "ugly" wall. It is possible to colorize your wall with what is generally known as "white washing" but by adding a cement additive you can tint it any color you would like. It's very simple really. You would need a bag of white portland cement, a bag of white hydrated lime and the colorant powder of your choice. Mix the portland and lime 3 to 1 and add water so it's a milk consistency then add the colorant until you get the color you like. Measure the colorant as you add it so subsequent batches will be mixed to the same color depth. Brush it on with a paint brush. The painting goes faster than you would think by sort of swishing the brush in all directions to fill all the little crevices, You have about 30 minutes or so to work the cement mixture but if it starts to stiffen just add more water and mix well again and finish up. I did this on my very old cement stucco house this past summer and it is the brightest shiny white you could ever imagine. It looks beautiful with freshly painted trim. Anyway this will work on anything with cement like texture (bricks too) and because of the added portland cement it will not wash away like a simple lime only solution will eventually do. You could even do a really bright color like red or deep blue if you wanted to and consider it an art wall if you wanted. Just something to consider in addition to plants. Any left over materials can be mixed with sand added to make stepping stones or cement planting containers etc. Good luck!
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If you were the national of any other country, you would just do it the best you can, expect the best, and not worry about things not working out. Because you're American, you're going to worry yourself sick about every bit of minutia. I would bet you could attack this in 50 different ways and it would be just fine. Honestly, your description is complicated. It would be much easier to understand if you'd show a few pictures of each thing you talk about. I suggest you post these pics and you'll be more likely to get some good advice.
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pls8xx
18 years ago
dorlando,

I don't seem to have mail from you. As far as I know the link on "My page" is still active.

I no longer monitor this site like I did in the past, and the amount of content I am willing to provide to gardenweb has been scaled back.

I haven't done an update this year on my wall project. Not much has changed in my method, except I worked out a nifty way of doing the forms for steps.

Here are a couple of pages that I did last year ....

http://www.geocities.com/pls8xx/construction.html

http://www.geocities.com/pls8xx/update.html

The vertical rebar consists of short bars in the footer that extend about 8 to 10 inches into the bottom of the wall spaced about 2 feet apart. These are positioned more to the backside of the wall. In addition longer vertical rebars are set in the footer about every 6 to 8 feet that extend to near the top of wall. These are used to hold the horizontal rebar and are positioned slightly toward the wall face. Walls 3 feet tall and above get a beefed up steel and footer treatment.
tabber174
Original Author
18 years ago
Sorry, that I didn't reply sooner. I was away over the weekend.

I haven't yet started my wall, so I don't have an answer for you.
gottagarden
18 years ago
COntact your local building codes dept. When I did they said concrete foundation should be 42 inches deep to avoid frost heave. Probably a little less deep in your area, but that is still deep! Probably not what you want to hear, it means renting an excavator for a day, but you also don't want to do all that work and have it buckle on you due to frost heave. Your local building codes dept will have the answers for you and they are free.

Concrete Block retaining wall

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pls8xx

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Concrete Block retaining wall

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