Earth pressure to resist overturning in shallow footings
Earth pressure to resist overturning in shallow footings
(OP)
I just had a conversation with an engineer who designs shallow moment resisting footings using passive earth pressure to help restrain overturning. The footings are for pre-fab buildings without a slab and the tops of footings are at grade. Rather than just increasing the footing size to eventually balance the overturning moments, he includes some passive resistance from soil against the sides of the 2'-6" footing. I have used passive pressure to resist sliding but using the pressure against the footing sides to resist overturning of an isolated footing is contrary to what I would call normal practice.
Does anyone have experience using this method?
David G. Smith
Smith Associates
Gainesville, GA
Does anyone have experience using this method?
David G. Smith
Smith Associates
Gainesville, GA






RE: Earth pressure to resist overturning in shallow footings
RE: Earth pressure to resist overturning in shallow footings
Also, unless the concrete was poured directly against the soil, requiring no backfill, the use of any passive pressure would not be allowed by code.
Mike McCann, PE, SE
RE: Earth pressure to resist overturning in shallow footings
RE: Earth pressure to resist overturning in shallow footings
And as ztengguy says, slab on grade concrete is one of the cheapest items in a project, pretty much just costing the delivered price of concrete ($110 per cu. yd. here), so using concrete to ballast a footing is pretty inexpensive.
RE: Earth pressure to resist overturning in shallow footings
Most Geotechs I know ignore the top 12 inches of what they call "fluff", a sophisticated term if I ever heard one. Or "duff" if you're in a forest.
Bob