Retaining wall

Old 11-14-10, 12:23 PM
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Lightbulb Retaining wall

I'm building a new home and have a significant slope to the land, about 4 1/2 ft from opposite corners so I'm building a concrete retaining wall around the house to have a small yard at house level and then straight drop to a second level yard. The retaining wall will have drains every so often. I'm paranoid about too much water collecting in the raised yard around the house putting a tremedous amount of water weight on the wall. My plan is to fill the raised yard, which will be about 15 to 20' out from the house, with clay then put plastic down which will be sloped a little toward a perforated drain pipe every 25 or 30' that will be surrounded by pea gravel, to help water run toward the drain and not allow water to go any deeper than the plastic layer, then cover this up with good top soil dirt to allow a good yard and flower bed. My question is am I creating other problems, such as trapping moister under the plastic, that would create mold or some other problem, or is this even a necessary step?
Old 11-14-10, 03:01 PM
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I would not try collecting water with a layer of plastic and directing it so far. I would put drains spaced every 2 or 3ft at the base your retaining wall. Even if one drain clogs another is not far away so little pressure can build behind the wall.
Old 11-14-10, 03:34 PM
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How high is the retaining wall and what is the construction and materials (reinforced concrete or segmental retaining wall block)? Concrete walls can get pricey and are limited to straight, level walls and plain surfaces.

All retaining walls must have a lower perimeter drain and backfill the is well draining as you seemed to mention.

A good wall does not require spaced drains if the is good backfill. A segmental retaining wall (SRW) will allow weeping of moisture if the backfill is not acceptable or is over-whelmed by moisture.

Clay is a "red flag" when it comes to retaining wall construction, even if it is "hard" when in place because it takes time to be acceptable.
Old 11-16-10, 09:14 AM
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Thanks for catching that. I had a poured wall stuck on my brain.

I have several retaining walls around my property that are made of dry stacked, pre-cast concrete blocks. None have drainage holes penetrating the wall but because of the cracks between the blocks the wall is free to drain as needed. Because these were engineered retaining wall systems they had very specific installation instructions/requirements encompassing foundation, drainage and backfill behind the wall. If you follow the manufacturers instructions it can be pretty idiot proof.

My one word of advice if you choose to use some sort of modular blocks for the retaining wall is to avoid the smaller, light weight blocks sold at many home improvement stores. Looking around town I see very few things built with them that stand the test of time. Bumps from lawnmowers, frost heave and poor installation seem to leave most installations looking bad in a short time. The "proper" engineered systems using larger blocks (usually 60lbs or more) with some interlocking mechanism seem to hold up much better in a addition to having a more professional look (when installed properly).
Old 11-16-10, 11:29 AM
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I built a 5' x 250' wall a few years ago and we used the small (30 # ?) blocks because there was no way we were going to lug that many 70 # blocks around

That said, the bigger blocks do make better walls but I would hire that done personally

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