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CONC - Footing Design

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If the soil above the footing is predictable there, I would use it to 
resist overturning, however, if the soil above the footing may be removed by 
man or nature, I would not use it to resist overturning.  (The footing would 
have to be designed for the load for when the soil *is* there.)

With regard to applying load factors, be careful!  The next to last paragraph 
in ACI 318-95 commentary R15.2 alludes to this being a problem.  What I 
typically do is hold the point of zero soil pressure under unfactored dead 
and live load and apply the load factors to the dead load soil pressure and 
live load soil pressure where the unfactored combined loading is maximum.  It 
seems that if you apply the load factors to either the applied loads, or the 
soil pressures resulting from those loads, you frequently end up with no 
uplift on the footing under factored loads.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona