EE WAS HAULING BOULDERS TO THE LEVEE IN THE EASTPIT, THEY HAD BEEN WORKING ON FOR A FEW MONTHS. THE LOADER OPERATOR HAD PUT ONE BUCKET IN THE BED OF THE HAUL UNIT FOR CUSHION WHEN THE OPERAT OR WAS ATTEMPTING TO PUT THE SECOND BUCKET ON THE TRUCK A BOULDER WEDGED IN THE BUCKET. THE BOULDER CAME FREE AND BOUNCED THE OPERATOR INSIDE THE CAB. EE WENT TO DR.4-8-02 & RELEASED TO WORK.