Design values for poles (smaller at the top and buried) and piles (smaller at the bottom and driven) are in the 2005 NDS Chapter 6. Design values for poles and piles were moved to the NDS Supplement: Design Values for Wood Construction in the 2012 Edition.
Other sources include the Timber Piling Council and National Frame Builders Association's (NFBA) Post-Frame Design Manual, visit http://www.nfba.org.
More information available at:
Timber Piling Council
Western Wood Preservers Institute
Standard Specifications for Wood Poles
Wood Handbook – Chapter 18 Round Timbers and Ties
See also: "Where can I obtain information on designing post frame structures (sometimes referred to as pole buildings or pole barns)?"