Retaining Wall Drainage Question/Concern

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Old 09-19-11, 12:58 PM
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Retaining Wall Drainage Question/Concern

Need to build a retaining wall, about 35 feet long tapering from 1 foot high....up to two feet then back to 1 foot. Replacing Railroad ties that were torn out to make way for new driveway. I cannot excavate area to the recommended width to allow 12+ inches to add drainage pipe and recommended gravel back fill due to property lines constraints.

Plan to use 12L x 4H x 8W interlocking block that will slope back toward the earth.

I have read/viewed on various DIY videos that walls two feet or less do not require extensive drainage systems (pipe, etc) and that minimum drainage considerations will suffice.

I will have about 4-5 inches to add gravel after the first 2 courses of block and as the wall comes up and tapers toward the earth, that space will diminish to 1 - 2 inches.

Again, max height is going to be 2 feet and the base of the wall will toe into 4 inches of 4000 psi mix concrete....very solid footing.

The railroad ties I am replacing did not display evidence of excessive lateral soil movement and/or hydro-static pressure, so I have a sneaking suspicion the area I am trying to contain drains really well on it's own and that what little I do in the way of adding gravel behind the wall will only enhance it.

Any info from anyone's experience working with constraints like this would be helpful.
 
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Old 09-19-11, 03:42 PM
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When you say "property line constraints" is it a setback issue or would you be excavating on your neighbor's property? Sidewalks, driveways, and below grade walls are not structures by definition and are excluded from setback restrictions here in the Land of Enchantment. If, when you're done, everything will be buried and replanted, talk to your neighbor and ask if it is a problem for them.
 
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Old 09-20-11, 06:42 AM
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My neighbors line is right there and I do not really want to "go there" regarding the property line. I think my home/property improvements efforts are starting to disrupt the neighborhood. (Brand new driveway took 5 weeks to complete...neighborhood up in arms!)

My main reason for posting here was to get some feedback regarding what I am now referring to as the "two foot" rule....meaning retaining walls that small do not require extensive drainage techniques. It just seems excessive to me that you would need to excavate up to two feet behind a retaining wall for a wall that will ultimately be no higher than two feet itself. But I am not a physicist or a soils engineer, so...

I guess I have pretty much convinced myself that what I am doing will work fine, especially since the earth behind the wall is not freshly moved or disturbed in any way. The house on the property is 50 years old and given the effort it has taking to excavate what I have to date (I have yet to lay the first block, 10 hours of nothing but digging it out.)....I would imagine the earth there has not been disturbed since that time. Also, the block I am using is designed to allow weeping, so the wall itself has drain capabilities.
 
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Old 09-20-11, 05:43 PM
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The instructions for my retaining wall recommended 6"12" of gravel behind the wall. I think it was ok to use 6" if it was up to a certain height. I can't remember what they said to do as far as piping. I know I opted to install a pipe behind mine even though it was less than 4' tall. I didn't want to risk any chance of failure of the wall since I was already replacing a failed wall. At 2', I don't think you need a pipe, but I would put at least 6" of gravel behind it. I see you are in TN so I doubt frost heave will be an issue for you.
 
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