Shallow Footings Bearing Capacity

[soildoc]

When calculating bearing capacity for shallow footings, in the various formulae (including Terzaghis) do I use drained or undrained parameters? For context, most of these calculations are done for clay. Most engineers are using undrained shear strength (and phi=0) to calculate bearing capacity, but shouldn't we calculate drained conditions as well using just friction angle?

 

[geotechguy1]

Rather than me giving the answer away, what I think you should do is calculate bearing capacities for a range of common footing sizes and embedment's in your area of practice, with undrained and drained parameters of clay of varying undrained and drained strength, and you may come to understand the answer that way.

 

[soildoc]

and I have. always end up with drained parameters giving approximately half of what undrained parameters would give. Which leads me to ask if I am being overly conservative using drained parameters? or if it's shallow footings in clay, undrained parameters will suffice as drained conditions won't realize?