Bearing Capacity Formulae For Clays

[GeoGrouting]

Assuming phi = o and saturated clay soil.

If a square foundation is at a depth of D, do we need to put bouyancy unit weight of soil to calculate(gama.D.Nq component?

q = 5.5 C Nc + (gama).D.Nq

 

[fattdad]

when using phi=0 ground water table is not an issue. Use your total unit weights. That said, I'd assume no depth of burial and just use 5.5*Su. Su is the undrained shear strength, which is technically different from cohesion.

Don't forget your safety factor - typically taken as 3.0.

f-d

¡papá gordo ain’t no madre flaca!

 

[GeoGrouting]

So does it mean that if the square footing would be at a depth of D or on the ground surface, it has no effect on the ultimate bearing capacity. Sorry, I may miss something here.

 

[fattdad]

No the depth of burial will factor into the design if you want it to. I just don't. Never know when something is going to get dug up, or a slab on grade replaced, or something else. . .

f-d

¡papá gordo ain’t no madre flaca!

 

[GeoGrouting]

Dear Fattad

Ok if I decided to take into account the depth of overburden in clay materials, should it be (gama)'D or (gama)D? Thank you again.

 

[BigH]

Me - I just use 2xSu and leave it at that - close enough. Then check the anticipated settlement and adjust your allowable bearing pressures from there.

 

[fattdad]

Again, I agree with BigH - exactly what I do also.

Regarding the qusetion of how to handle the depth of burial, if you are looking at undrained conditions, you have to use total loads. So, that'd be gammaD.

f-d

¡papá gordo ain’t no madre flaca!