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Re: Passive pressure on retaining wall key

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I don't use Amrhein's method. I go by the conservative method that uses
passive pressure that starts at zero at the top of the soil near the toe and
extends to the level of the bottom of the key, regardless of key location or
soil pressure. I checked my textbook"Foundation Analysis and Design" by
Joseph Bowles, Second Edition, page 380, and the sketches of the passive
presure diagram shows it the way I do it.

Unless somebody shows me a textbook or report prepared by a geotechnical
engineer experienced in passive pressures on soil which says otherwise, I'll
stick with my method.

I believe soil is a a complex structural material that does not follow the
behavior of our common structural materials such as wood, concrete,steel,
masonry, etc. I assume that geothecnical /soils engineer are the experts on
these and leave it up to them to guide us in what pressures and how these
pressures act on our footings and keys to resist design loads.

However, using Amrhein's method will not cause failure, I think, because the
design method is conservative anyway. The passive pressure given by soils
engineers in their report already has a high factor of safety, the friction
coeficient also has a factor of safety, plus again the required 1.5 factor of
safety against sliding and again considering that the active pressures  given
by soils engineer is also conservative, and also that these active pressures
are again reduced as the wall moves in a cantilever retaining wall. 

Ernie Natividad