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Wednesday, July 27, 2011


I have received several inquiries about building retaining walls. While there is alot of information out there, some of it is contradictory, so I will tell you what I find works best for me.
  •   Foundation Trench: The foundation trench should be dug deep enough to remove all organic matter or black soil. Once this is done another consideration for foundation trench depth is the eventual height of the wall, the guide that I use is.
  • Trench Depth: The depth of the trench should be between a third and a half of the height of the wall. Therefore if the wall is to be three feet high then the trench should be between twelve and twenty four inches deep. I use the same calculation for the width of the wall or the depth you need to dig back into the bank, plus at least a further twelve inches to allow room to back fill with clean crushed stone between the finished wall and the soil embankment.  I use three quarter inch clean crushed stone for the backfill and for filling the foundation trench.
  • Trench Width: The trench should also be three to six inches wider than the wall, this allows the foundation stones to be set in from the edge of the trench. When the trench is dug, fill to within six inches of grade with clean crushed stone then commence building the wall. I like to build a wall with two faces similar to a free standing wall but I reserve the poor quality stone for the side facing the embankment as this will not be seen when the wall is backfilled.
  • Batter/Slope of Wall: The batter or the amount the wall should slope into the bank is a personal choice, I use a batter of six to one, so every six inches of vertical wall building you should slope the wall toward the soil embankment one inch. If the wall is three feet high then the top will be six inches in from the vertical.To achieve this, set a frame at the correct angle at either end of your trench and string a taut line between the frames. Starting near the bottom and lifting the line as the wall rises, making sure the stones placed on the wall never rest against the line. This will give you a nice straight wall with a uniform slope.
  • Curved Walls: If the wall is to be curved, then I use lengths of rebar set at the correct angle every three to six feet depending on the severity of the curve.
  • Soil Considerations: If your soil is clay and if it is feasible I would advise laying a drain pipe from the base of the trench so the trench never fills with water which could be a problem in areas with freezing winters.   

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