calculating skin friction of pile with alfa method

[ketanco]

The term Cu in the fs=alfa x cu

this is the undrained shear strength, that I know. does this also mean the cohesion of that soil?

i ask because, to obtain cu, from other questions, i also remember dividing undrained strength by two, but that was the axial strength q-undrained and not the shear strength correct?

so in other words,

cohesion-undrained = shear strength-undrained = (axial strength - undrained / 2)

correct?

 

[civilized_naah]

For a saturated clay, for which the shear envelop is horizontal, the shear strength is the cohesion (y-axis intercept on the shear strength vs. effective normal stress graph). This being the radius of the Mohr's circle, is half the unconfined COMPRESSION strength (x-axis intercept of the Mohr's circle). Thus, the unconfined compression strength (which is sigma.not tau) is the diameter of the Mohr's circle and thus,

cohesion = half of unconfined compression strength

NOT

cohesion = half of shear strength