which depth to take for a basement footing for bearing capacity
which depth to take for a basement footing for bearing capacity
(OP)
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
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





RE: which depth to take for a basement footing for bearing capacity
Mike Lambert
RE: which depth to take for a basement footing for bearing capacity
FYI for these kids of problems the best thing to do is draw it out. I do it for all my actual problems and for the PE.
RE: which depth to take for a basement footing for bearing capacity
Mike McCann
MMC Engineering
RE: which depth to take for a basement footing for bearing capacity
RE: which depth to take for a basement footing for bearing capacity
in response to above questions:
mssq: yes there is concrete slab
phidelt: my reasoning was, that depth was subject to all 10 feet of soil loading in the past. thats why i took 10 feet. so a building that has footing 2 feet below natural ground and a building that has footing 2 feet below the ground which is 8 feet below original ground must be different - i thought
RE: which depth to take for a basement footing for bearing capacity
The only reason that the solution would use 2 feet is using the assumption that the slab will offer no confinement. As a practical matter, I would check it both ways and design the slab to achieve confinement.
RE: which depth to take for a basement footing for bearing capacity
RE: which depth to take for a basement footing for bearing capacity
RE: which depth to take for a basement footing for bearing capacity
RE: which depth to take for a basement footing for bearing capacity
RE: which depth to take for a basement footing for bearing capacity
RE: which depth to take for a basement footing for bearing capacity
I think when it comes to the lab they are referring to more in depth analysis of the soil and horizontal forces acting on the slab rather then the basic bearing capacity. If there was no slab then this would not really be a bearing capacity question it would be more of a pile question. Such as in alaska we have houses elevated on helical anchors rather then on slab and grade foundation.
RE: which depth to take for a basement footing for bearing capacity
RE: which depth to take for a basement footing for bearing capacity
Maybe some sketches will help. Look at this webpage: http://wwweng.uwyo.edu/classes/fa2013/ce3600/11_fo...
RE: which depth to take for a basement footing for bearing capacity
RE: which depth to take for a basement footing for bearing capacity
Several people mentioned that the failure surface occurs on either side of the footing. Perhaps I misunderstood kentanco's replies. But, I thought that kentanco may not remember the mechanism of the failure for a typical case with soil balanced on both sides. That is why I posted the link.
RE: which depth to take for a basement footing for bearing capacity
RE: which depth to take for a basement footing for bearing capacity
RE: which depth to take for a basement footing for bearing capacity
RE: which depth to take for a basement footing for bearing capacity
The removal of soil means you have to consider PVR. But you do NOT count that soil for current overburden.