Typically, we start with partial safety factors—2 for skin friction and 3 for tip resistance—and then do a final check with a global safety factor between 2 and 3.5. Global FS depends on your information; it’s a function of soil conditions, how comprehensive the site investigation was, and what type of tests were performed.
NHI has a manual on drilled shafts.
I’m not a geotech or bridge person…you’ll get a better answer from a geotech or a bridge person.
