which depth to take for a basement footing for bearing capacity

[ketanco]

Hello,
I am preparing the civil PE exam in geotech and in the NCEES Geotechnical afternoon sample questions, question 520, for the depth while calculating the D, why do they take 2 feet and not 10, which is (2+8) feet up to the overall ground surface?

for the ones that do not have the book, the question asks bearing capacity of a footing in the basement of a building. the footing is 2 feet below the basement ground level, but it is 10 feet below the overall ground level around the building. i calculated using 10 feet, but in the solution it calculates by taking 2 feet only and i dont know why.

Thanks

 

[Althalus]

You're conflating overburden with PVR. This is a common mistake.

The removal of soil means you have to consider PVR. But you do NOT count that soil for current overburden.