Checking of soil pressure against allowable bearing pressure

[ramihabchi]

Allowable bearing pressure by definition is the least between the allowable bearing capacity for shear failure and that for Having excessive settlement.
By excessive settlement they mean total settlement right?I mean having soil pressure below the allowable wont let me go on without checking differential settlement.
my second question:
Shear failure happens in a failure mechanism in which it depends on the total ultimate load and not on each point's pressure.So I think checking soil pressure to prevent shear failure based on a finite element software will be too conservative(having all point's pressure <qult),and it is better to compare mean soil pressure with bearing capacity.I was in doubt if this is correct but what made me convinced more is the definition of bearing capacity I have found on the internet:it is the average soil pressure that can be beared without shear failure.So am I right?I can only compare average values?

 

[BAretired]

[li]If the soil pressure is below the allowable, it means differential settlement will not be excessive.
[/li]
[li]It is usual practice to ensure that no part of the foundation causes a pressure in excess of allowable. In the case of a retaining wall footing, the pressure may be trapezoidal or triangular, but the maximum should not exceed the allowable pressure.[/li]

BA

 

[r13]

Just wat to point out that the settlement reported by the program is the displacement caused by the point load over the tributary area with unit stiffness. As the FE getting finer, the settlement is more realistic; when coarser, it approaches straight line (stresses averaged out). I was more concerned with the absolute difference between the peak and minimum between two structural elements, or even within the same structural element under consideration, that may exceeds the limit set for differential settlement, but if I kept every element with stress below the allowable bearing strength, then I knew there was no need to worry. How to interpret FEM out puts somehow is largely based on engineering judgement, as opposed to the case (linear approximation) pointed out by BA, which in nowhere the bearing stress can be exceeded.