HAUL TRUCK WAS DUMPING ROCK ON STOCKPILE. AS BED WAS BEING RAISED, TRUCK WENT OVER SIDE OF STOCKPILE, DOWN THE SLOP AND CAME TO REST AT TOE OF PILE. DRIVER WAS WEARIGN SEAT BELT. CONTRIBUTING CONDITIONS INCLUDE DRIVER PROCEEDING TO DUMP WAS TOO CLOSE TO EDGE AT AREA OF STOCKPILE WHERE BVERM HAD SLUGHED. THE TRUCK'S CATWALKS, HANDRAILS, CAB DOOR AND WINDOWS WERE DAMAGED.