Mixed (Cohesive and Granular) Soil Properties

[hamilto4]

I am designing sheeting in soils that have both cohesive and non-cohesive properties. I am having trouble when comparing my hand calcs to the Pile Buck output (mostly the active and passive pressures). I have the Pile Buck Design manual that shows step-by-step procedures for either all cohesive soils or all granular soils, but nothing with a mixture of the two. An AASHTO design manual states that for the active pressure, you subtract cohesion (2*C*sqrt(Ka)) and for the passive pressure you add cohesion (2*C*sqrt(Kp)). I guess my questions are how does pile buck account for cohesion in mixed soils, and what are the active and passive pressures in a mixed soil?

 

[civilperson]

For fines greater than 20%, use cohesive values for piles, ka and kp.