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Re: Footing design for uplift

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That's a reasonable point - 60 degrees is an easy number, too. I'll admit that I usually only count about half the anticipated cover for variable final grading. If they get the grading right, then the soil wedge outside the footing will have the same net volume as if I'd used 60 degrees and the full fill. Plus the soil density and concrete weight are pretty well known numbers to count a 0.6 factor in the load combinations.

Experience also says that you rarely see PEMBs rolling down the road on their undersized footings.


Jimenez, Jorge A. wrote:
Jordan, I am not sure if 45 deg is in the safe side for the problem. As
in the retaining wall analysis, the soil failure plane is not at that
angle. Note that geotechs uses K, coefficient for lateral pressures, in
their formulas. Bowles in 'Foundation Analysis and Design' shows the
shape of the failure zone, and that shape is a curve. For this curve the
average slope appears to be greater than the slope with 45 deg. I prefer
60 deg respect to the horizon as a easy and conservative approach.



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