THE SHOTCRETE CREW WAS ATTEMPTING TO SHORE UP A BAD GROUND CONDITION. THE BACK BEGAN TO DRIBBLE, CREW PULLED OUT AND WAITED. THE BACK CAME DOWN AT THE 21-055-29G AT APPROX 1105 AT APPROX 20' F ROM THE FACE A 20' SECTION FELL OUT ABOVE THE BOLTS APPROX. 720 TONS.