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Gravity wall

Discussion in 'Hardscaping' started by Remington351, Aug 8, 2011.

  1. Remington351

    Remington351 LawnSite Member
    Messages: 34

    I've got a couple of questions about a retaining wall that I need to replace. I'm a homeowner and I'm hoping to tackle this myself so any advice would be appreciated.

    I'd like to replace a failing 4ft tall by 40ft long pressure treated wall. The problem I have is that I have mature landscaping (plants, bushes, etc) that starts 3ft-4ft behind the wall. Ideally I'd run 6ft of miragrid to ensure that the wall outlives me, but in this case I'd really like to avoid tearing out all that landscaping in order to place geogrid.

    I know that most systems Versalok, Keystone, AB have a 3ft-4ft gravity wall limitation depending on soil conditions ...mine is very red and very clay filled..which I'm thinking would put me at the upper limit of the recommended design envelope. So I was curious if any of the following procedures would help ensure the integrity of a gravity wall.

    1. Instead of the standard 12" of 3/4" stone backfill I extend the backfill distance out by 2 or 3 feet? My feeling is that the additional stone backfill will eliminate any additional water loading. Thus ensuring the longevity of the gravity wall because now I've essentially moved the soil loading from 1 foot behind to 3 feet behind the wall? Yes? No?

    2. What if I overbuild the CR8 leveling pad to be deeper and wider? Will this help?

    How about burying an additional base course of SRW units? Instead of the typical 6" buried depth for the first row what if I bury two rows? or three?

    I realize that any or all of these steps will increase my materials cost, but if I could avoid replacing all that landscaping it would be worth it.

    Thanks for the help.

  2. White Gardens

    White Gardens LawnSite Fanatic
    Messages: 6,776

    Do you have room to install the new wall out farther from the original? That would be my only good guess on how to save the landscape.

  3. Remington351

    Remington351 LawnSite Member
    Messages: 34

    Thanks White Garden, but no, I can't move the wall out. There's a door about 14" from the existing wall preventing this.
  4. landscapedesignpros

    landscapedesignpros LawnSite Senior Member
    Messages: 337

    go with a 10" base compacted in 1" lifts thats 3' wide put woven driveway stabil fabrick under the base.DO NOT OVER EXCAVATE. your base should be as hard as concrete when your done. place the wall in the middle burry a full course and a half, use your plan of placing drainage rock 3' deep behind the wall. Make sure to put 2 tiles behind your wall, one at the front that drains through the face via grates and a rear one that dumps out on each side of the wall. make sure to shoot them so they drain. If there is any suface loading above the wall this will not work but if its just a flat landscaping bed and your soil is solid clay , no rocks or gravel mixed in and you can keep all water logging out this should move the sheer line of the clay far enought back as to be ok and the wall should be ok so long as there is no hydrolic pressure building up. if there are any gutters or any roof lines that dump water on top of this wall that will need to be controlled. hope this helps
  5. DVS Hardscaper

    DVS Hardscaper LawnSite Fanatic
    Messages: 6,576

    Red Clay Soil? Are you in Emmittsburg?

    One guy wrote to do a 10" base. The base has NOTHING to do with the surcharge behind the wall. No disrespect intended.

    Making the drainage chimney 2' instead of 1' will not work either. We did a small wall at my neighbors a few months ago. Nice, compactable soil, and not a spec of clay. Perfect soil for building walls. 5' high, with very little load behind it, and we still installed 2 or 3 rows of grid. IT'S CHEAP INSURANCE.

    Burying additional courses will NOT help either.

    I did a retaining wall estimate in Bethesda Sat morning. The guy had a NICE old cherry tree with roots in the area where grid would go. He was not happy when I said that we would damage the tree's roots. I said to him (in a nice, professional tone) "you'll have to choose either the wall or the tree".

    Same goes for your landscape plantings. Life sometimes has sacrifices. Drives me up the wall when people expect us to work magic to save some plants that are easily replacable. They're so used to smart phones and apps where you push buttons and have everything at your fingertips, that they sometimes do not live in reality :)

    You can go with Keystone Standards and double them up......but you still have to excavate nearly the same amount of earth.

    I doubt your 4' wall will need 6' of grid. The rule of thumb is that grid length is usually 80% of the wall height. Although an engineer may spec otherwise.

    Last edited: Sep 13, 2011
  6. DVS Hardscaper

    DVS Hardscaper LawnSite Fanatic
    Messages: 6,576

    Also, if you're in MD no need to use Versa-loc, Keystone, or Allanblock.

    The best block available in MD is Cornerstone. No pins, clips. As user friendly as it gets.

    Manufactured by York Building Products in Frederick, which they have dealers all over MD that sell their block.
  7. AztlanLC

    AztlanLC LawnSite Bronze Member
    Messages: 1,050

    I also think you don't need 6' grid, hire an engineer or go to unilock's web site they have cross sections for all type of walls and soils, that would give you a reference to start, they also have the sienna stone wall that you can build without grid for that size.
    Also most manufactures can do preliminary drawings
  8. all ferris

    all ferris LawnSite Bronze Member
    Messages: 1,309

  9. DVS Hardscaper

    DVS Hardscaper LawnSite Fanatic
    Messages: 6,576

    Most *home owners* do not have the equipment to set a 1200# block.

    And it's 28" wide. So by the time u install drainage, you've done had to dig more than you would have to dig for grid for a 4' wall...
    Posted via Mobile Device
  10. zedosix

    zedosix LawnSite Silver Member
    Messages: 2,665

    Imo I would construct your wall as per specs and not worry about 3' of drainage, I would use a bottom drain daylighted of course, use the same clay on the top 6" of back fill and slope towards the front. You want water to run off this wall, not behind it. Bury approx. 15% the total height of wall, which would be roughly 1- 1.5 blocks.

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