OPERATOR ON THE 637 SCRAPER WAS RETURNING TO BARROW PIT AFTER DUMPING HIS LOAD. THE AREA OF THE RETURN ROAD THAT OPERATOR CHOSE TO RETURN ON WAS BEAT OUT FROM PRIOR TRAFFIC. OPERATOR WENT THROUGH 3 WELL DEFINED POTHOLES, JARRING HIM. THIS RESULTED IN A FRACTURE TO THE 12TH VERTEBRAE. EMPLOYEE WAS TAKEN OFF WORK.