EE WAS BACKING UP A 35 TON DUMP TRUCK TO DUMP A LOAD OF BARITE. WHEN THE DUMP WAS RAISED THE GROUND TURNED LOOSE UNDER BACK TIRES. TRUCK FLIPPED OVER HIGHWALL AND FELL APPROX 30 FT LANDED UPSIDE DOWN. 911 WAS CALLED & EE WAS TAKEN TO ER ROOM. EE REC'D BROKEN LEFT ARM & COMPLAINED OF LOWER BACK PAIN