TRUCK DRIVER LOST AIR PRESSURE IN BRAKE SYSTEM NEAR THE TOP OF THE RAMP AFTER DUMPING AT THE PRIMARY CRUSHER. DRIVER ATTEMPTED TO STOP THE TRUCK BY SHIFTING TO REVERSE. THIS STALLED THE ENGINE AND THE DRIVER LOST CONTROL. THE TRUCK ROLLED ABOUT 580"", THROUGH A BERM, OVER A 32"" WALL, LANDED ON ITS NOSE AND FELL TO THE RIGHT SIDE. DRIVER WAS WEARING A SEATBELT.