Gross allowable bearing capacity of soil
Gross allowable bearing capacity of soil
(OP)
Can anyone explain about a term "gross allowable bearing capacity" of soil for building foundations. How does it differ from allowable bearing capacity , or net bearing capacity ?
I assume that the term "allowable" means that a factor of safety is inherently included in the value (instead of ultimate bearing capacity), but what is the significant of the word "gross" ?
Thanks
I assume that the term "allowable" means that a factor of safety is inherently included in the value (instead of ultimate bearing capacity), but what is the significant of the word "gross" ?
Thanks





RE: Gross allowable bearing capacity of soil
However, I also have a question I have about this concept. Using this logic, the lower you place the footing, the lower the net bearing capacity of the footing is because some of the capacity is used up by the soil on top of the footing. Now, I'm not a geotechnical expert (and I don't even play one on TV), but it seems like the capacity should not decrease (or should even be better) because of the confining effect of the surrounding soil. Can any dirt expert shed some light on this?
RE: Gross allowable bearing capacity of soil
RE: Gross allowable bearing capacity of soil
Hope this helps some!
Carl
RE: Gross allowable bearing capacity of soil
An important point is that bearing capacity taken from in-situ testing (SPT, CPT, Pressure cell etc.) begins as Gross Bearing, as the soil trength considerations are direction addressed. Initially, the soil overburden (and in some cases, existing foundation loads) is considered.
Consolidometer (settlement) testing begins as Net Bearing, as settlement limitations are addressed. Remember that settlement is caused by Net increases in applied load.
There are many references but only a few that provide easily understood definitions, along with discussion which illuminates the issue and presents potential pitfalls.
B.K. Hough, Basic Soils Engineering, 2nd Edition, 1969, provides a good discussion in chap. 9, without going into how the actual bearing values are obtained.
A.S.C.E., Bearing Capaity of Soils, Technical Engineering & Design Guide,()US Corps of Engrs., 1993 provides a useful set of definitions, good discussion, methods of computation and a good bibliography.
C.G.S., Canadian Foundation Engineering Manual, 3rd Edition, 1992. Chaps 8, 9 & 10 directly addresses the question.
Fellenius, Basics of Foundation Design, 2nd Edition, 1999, provides discussion which is to the point.
Sorry for the length.