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should i use net or gross soil pressure for this foundation

should i use net or gross soil pressure for this foundation

should i use net or gross soil pressure for this foundation

(OP)
The vendor for the equipment also provided the foundation.
When I back check the foundation, I'm a little confused if I should check their specified minimum soil bearing to net or gross pressure.
If I compare it to gross, the foundation is failing in soil bearing.
I'm also concerned the bearing area is just 52%.

See attached pdf for my calculation.

RE: should i use net or gross soil pressure for this foundation

(OP)
I think I'll just comment on the vendor foundation notes to specifically say Allowable Net Bearing Pressure.

What is your opinion about 52% only bearing area?

RE: should i use net or gross soil pressure for this foundation

Yes, it would be about 2500 psf gross, or 2000 psf net soil pressure. I wouldn't worry about the triangular soil pressure, unless the moment is a permanent loading condition. Maybe you need to confirm that the soil at the site is better than that, as most soil 4' below the surface is.

RE: should i use net or gross soil pressure for this foundation

I'm not sure where that allowable came from....but if it came from a geotechnical engineer, I'd contact him/her and explain the situation. Most of the time when geotechs figure a allowable bearing capacity.....it is based on equations that include the overburden (i.e. everything above the foundation level). Ergo they are giving you the gross capacity. (Settlement is typically based on the net pressure.)

Maybe that pressure is based on a load at the surface and maybe it isn't (not sure what your frost depth is). But I'd clarify it.

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