Increase in allowable pressure for depth of footing thread255-24941
Increase in allowable pressure for depth of footing thread255-24941
(OP)
There is a statement in this string from 2002 by the OP that after the first twelve inches the allowable soil bearing can be increased 20% per foot of depth up to 300% of the initial soil bearing value.
Is there a reference section in the IBC or IRC to verify that? I have never seen it there... yet.
Is there a reference section in the IBC or IRC to verify that? I have never seen it there... yet.

Mike McCann, PE, SE (WA)






RE: Increase in allowable pressure for depth of footing thread255-24941
RE: Increase in allowable pressure for depth of footing thread255-24941
What I know is that, if you have a net allowable soil bearing strength, it is usually specified at a given starting depth, ie. 3000 psf at 3ft depth. If it is a "net bearing capacity", net never changes, so absolute soil bearing at a different depth can be increased by the weight of soil that overlayed that depth. Absolute bearing capacity at 6ft would be 3000_psf + overburden above ie. (6_ft-3_ft) * soil density_pcf
3000psf + 3ft * 110pcf = 3330 psf at 6ft.
RE: Increase in allowable pressure for depth of footing thread255-24941
I just cannot find it in the code - it may come from some other publication or an inventive Geotech. I know I have seen something like this used in the past, but could never justify it in writing.
I think it possibly could be justified by the passive restraining effect of the adjacent soil, preventing the rotational soil failure seen at shallower depths. At least that would make sense to me.
Mike McCann, PE, SE (WA)
RE: Increase in allowable pressure for depth of footing thread255-24941
RE: Increase in allowable pressure for depth of footing thread255-24941
RE: Increase in allowable pressure for depth of footing thread255-24941
Mike McCann, PE, SE (WA)
RE: Increase in allowable pressure for depth of footing thread255-24941
RE: Increase in allowable pressure for depth of footing thread255-24941
The situation becomes a very moving experience.
Mike McCann, PE, SE (WA)
RE: Increase in allowable pressure for depth of footing thread255-24941
RE: Increase in allowable pressure for depth of footing thread255-24941
Was Yoda your teacher in school?
Mike McCann, PE, SE (WA)
RE: Increase in allowable pressure for depth of footing thread255-24941
That was not a good day.