While performing stability analysis of dams, we have a "shear friction factor" for which we need cohesion value of the material. I am confused that whether i should use cohesion value of concrete or the rock foundation? What is the cohesion value of 3000 psi concrete and how to calculate it? In the book of santosh kumar garg, he has used the shear strength of joint instead of cohesion. Why is that? Because many other books use cohesion in the formula.