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Old 07-18-2010, 05:54 PM   #1
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Retaining wall


Hello everyone
To flatten my 50 feet wide backyard I need to do some excavation and build retaining wall (I am gono hire professionals). I was going to do what my neighbour had done which is 2 step retaining walls (made by 6x6 timbers) each 4 foot high, but I found out that the 2 retaining walls are only 5 feet apart. As far as I know the distance between two retaining walls must be twice their height in order to function. So my question is that, if there is really no room to build these 2 walls 8 feet apart, can I just get away with only one wall as the second one might not function any ways… my second question: Is it safe to build a wall higher than 4’, say 6’, by anchoring more deadmans?

Thank you in advance

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Old 07-18-2010, 06:22 PM   #2
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Retaining wall


How you can build the wall will depend a lot on the soil conditions you have on the hill behind you. You can call in a soil engineer to get recommendations as well as contractors who have experience in building these structures.
Ron

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Old 07-18-2010, 08:11 PM   #3
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Retaining wall


In MA any retaining wall 6 feet or more in height must be designed by a registered professional engineer. I am not clear where you live, so I don't know the regulations where you are. However, you are incorrect in believing that it is essential to have a setback for the second wall equal or greater than the height of the lower wall. The required setback is a function of the type of wall.

You may want to look into segmental block retaining walls, very attractive, reasonable cost, and can be built with no setback between two walls. However, at 8 feet, they are going to require reinforced earth technique (this means metal or fiber straps that extend into the backfill perpendicular to the wall). This may not be possible if you are unable to excavate an adequate distance behind the wall, in which case you need to use a more complex, expensive technique.

Personnally I do not like wooden retaining walls, regardless of the techique used to treat the wood, it is not going to last more than 20 years, in many cases it is failing after less than ten years, which causes huge problems for the owner when the wall starts to collapse. A properly built concrete or segmental block wall will last 100 years at least.
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Old 07-19-2010, 02:52 PM   #4
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Retaining wall


Thank you very much for your comment Daniel. I am going to take your advice and go with segmental block. In your comment you mentioned something about setback being a function of type of wall; in my situation with a slope almost 45 degrees, 50’ wide and depth of backyard being almost 30’ can I get away with one 6’ high segmental block retaining wall or I must do 2 steps? What about wooden wall? Attached is a little sketch.

Thanks
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Retaining wall-backyard.jpg  
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Old 07-19-2010, 07:45 PM   #5
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Retaining wall


If your sketch is anywhere near accuracy, you REALLY need to have an engineer, or at the minimum a rep from the segmental wall manufacturer, take a look at your sight to OK what you want to do. There is a huge surcharge load on that wall, and will definately need some detailing on the re-inforcement. Geo-grid (which is one of the earthen reinforcement Daniel mentioned) is a viable option, but where, how much, how large, how often, etc.... needs to be determined by someone with the knowledge to do so.

Good luck.
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