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Thoughts on Wall Drainage

Discussion in 'Hardscaping' started by steve5966, May 7, 2008.

  1. steve5966

    steve5966 LawnSite Member
    Posts: 210

    This thread isn't about how to do drainage, but why we do it like we do.

    This came about while building a large wall last fall. I was talking to the engineer who designed the wall and just making sure everything was right. I mentioned that we daylighted the draintile every 20 feet and questioned why so close together ? This is when it got interesting for me. The engineer asked if I had ever seen water come out of one? I replied that I had seen a trickle but nothing more. He replied that if I saw water flowing out that I should run and run fast. Of course I asked why and this is what he told me. Drain tile behind a wall does absolutely no good, but they still use it because it is common practice. If their is enough water behind the wall to flow out, not just trickle, the hydrostic pressure will blow out the wall. I should have asked for a more technical reason, but I was too busy to discuss it.

    I have been thinking about this for months now and it does make sense. We place the tile on packed ground and cover it with rock that will let the water flow. To get water into the tile and flowing it needs to be at least an inch deep. (remember the corrigated tile is not smooth inside) If the tile is sloped for drainage, the water will flow through the rock before it is deep enough to enter the tile. With this, the water will enter the tile at the lowest point. At the same time it will flow between the block and depending on the block your using, through the center of the block to your base.

    Any one else have any thoughts on this?

    To try to stop the pointless comments and repeating what books and manuals say, I am certified and i've stacked a block or two.

    If you want to see the wall that started this, search here for Manta Ray earth anchor.
  2. LawnVet

    LawnVet LawnSite Member
    from SE MI
    Posts: 220

  3. mrusk

    mrusk LawnSite Gold Member
    Posts: 3,260

    I will tell you one thing, you will learn more about walls talking to a engineer then anyone else.
  4. PlatinumLandCon

    PlatinumLandCon LawnSite Bronze Member
    Posts: 1,315

    I'm looking forward to doing my first engineered wall... the tallest I've done is about 18" so I've never needed it all planned out.
  5. Total Landscape Solutions

    Total Landscape Solutions LawnSite Member
    Posts: 190

    Years ago when doing large commercial work I was a laborer on a very large, engineered retaining wall. The stone back fill alone was estimated at 2,225 tons. I remember the grid lengths were 11'6", because I cut every one. Wall was 13' in height and I think around 150-175 lnft.

    I remember talking to the engineer, who was working with us every day, when we installed the drain behind the footer. His comment was "It'll be years before this pipe even sees a drop of water."

    The longer I am in the field I wonder the same thing about the drain. I would totally agree about water flowing at a high rate out of the footer drain. If I saw one really flowing, I'd run.

    I'd love to hear more about this from and engineer who really knows. Anyone know one who may be able to respond to questions like these in this forum?

    Good thread steve
  6. steve5966

    steve5966 LawnSite Member
    Posts: 210

    I really thought this would get more discussion, but maybe everyone is still too busy.

    Musclecarboy, when you do a engineered wall be sure that you document the construction process. Take notes and photoraph the complete process, if anything goes wrong it will be you against the engineer. Nothing against engineers, but I've seen guys go out of business over the blame game on a failed wall.

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