Posted by Ples E. Schnitz on March 06, 2002 at 14:34:48:
I'm with Paul. You really should not be designing footings!
1.You don't know the bearing capacity of the soils.
2. You don't realize that sandy soils have a recessive quality rather than expansive.
3. Best case bearing capacity of compact course sandy soils is 2000#/sf, meaning area of your spread footing would be 62.5 S.F.
4. You do not understand the principal of beam on elastic substrate-footing cannot be 12" thick at this area, or more than 60% would "curl up and be non-contacting resulting in failure within 3 seconds. There is a very emperical ratio of area to thickness of spread footings.
Find a structural engineer-fast.