The perimeter calculation and assumptions are always a question for H-Piles. When you calculate the perimeter with the assumption of plugged , the perimeter would be less ( gross perimeter of H-pile , so one will get low skin friction, high end bearing) . When you calculate the perimeter with the assumption of unplugged , the perimeter would be more ( interior web and flange surfaces H-pile also considered ) , so one will get high skin friction, low end bearing ...After static test , still the contribution of end bearing to the total resistance is unknown..
IMO , the best practice, do both analyses (unplugged and plugged) and use the lower value for design.
EDIT: I have a problem with with this forum.. I have added the print screen. The letter size is less than 5 and hardly readable.This problem is only at ENG-TIPS forum.. Any suggestions?