Gross vs net allowable bearing capacity

[Tstruct]

I have 2 different soil investigation reports for the same site. One done 3 years ago and one recently. One of them provided gross allowable bearing capacity while other provided net allowable bearing capacity. The structure doesn't have any basement, just simple isolated foundation.
If I use net bearing capacity then should I ignore overburden soil load?
And If I use gross bearing capacity then should I consider overburden soil load.
Am I thinking right? or correct me and provide reason please.
Thanks

 

[JAE]

The way a good geotechnical friend of mine explained it to me many years ago:

If you are given a NET Allowable Bearing Pressure:

1. Think of that little piece of dirt that will be located just below your footing.
2. Before any construction - what overburden did that little piece of dirt have over it?
3. Assume - or find out - the density of that overburden soil over your LPD and calculate the existing overburden pressure (EOP)
4. After your new construction removes any portion of that EOP your net allowable bearing pressure would be increased by the EOP.
Example - you are given a net allowable bearing pressure of 1,500 psf. - Your new footing will be located in the bottom of a basement which requires the removal of 9 feet of soil with a density of 100 pcf to achieve the bottom of footing elevation. The 9 ft of soil = 900 psf pressure. Your allowable bearing pressure is 1,500 + 900 = 2,400 psf. You would include the self-weight of your footing, the structural column load on it and any minor overburden over the footing to determine the applied pressure to the "little piece of dirt" below your footing.