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Unconfined strength and Net all. bearing value
- Thread starter WWTEng
- Start date
If you are running the unconfined compression test, I'll go ahead and assume that you are dealing with a fine-grained (i.e., cohesive) soil. Therefore, let's discount any contribution from internal friction.
According to the Terzhagi equation, for phi=0 (as appropriate for soils without internal friction), Nc=5.7 so qult=cNc. For undrained analyses, c=Su (cohesion equals the undrained shear strength. Undrained shear strength is equal to one-half the unconfined compressive strength.
So, ultimate bearing pressure would be:
qult=5.7*qu/2 or qu*5.7/2 or 2.85*qu
If you consider a safety factor of 3 q-allowable is then equal to:
q-allow=0.95*unconfined compressive strength. Heck that's about like saying the allowable bearing pressure is equal to the unconfined compressive strength!!
Wow! That was easy, eh?
f-d
¡papá gordo ain’t no madre flaca!
According to the Terzhagi equation, for phi=0 (as appropriate for soils without internal friction), Nc=5.7 so qult=cNc. For undrained analyses, c=Su (cohesion equals the undrained shear strength. Undrained shear strength is equal to one-half the unconfined compressive strength.
So, ultimate bearing pressure would be:
qult=5.7*qu/2 or qu*5.7/2 or 2.85*qu
If you consider a safety factor of 3 q-allowable is then equal to:
q-allow=0.95*unconfined compressive strength. Heck that's about like saying the allowable bearing pressure is equal to the unconfined compressive strength!!
Wow! That was easy, eh?
f-d
¡papá gordo ain’t no madre flaca!
FixedEarth
Geotechnical
Nice explanation fattdad.
I might add, also check settlement & differential settlement, since it can lower your design allowable bearing pressure.
I might add, also check settlement & differential settlement, since it can lower your design allowable bearing pressure.
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