The employee was operating a D-10 bulldozer pushing coal on the D Bench coal stock pile west to east across feeder A. While pushing coal across the feeder the back end of the dozer fell approx. 8-feet into a void above Feeder A. The dozer was not able to pull out of the hole and was stuck. The employee was able to climb out of the dozer and walked off of the stockpile unhurt.