Found during the preshift examination prior to the start of 3rd shift.Mine was idle at the time of the fall. Fall located in #5 1st west entry at 22+20. Fall was 17'l, 18' w, 12' thick. The area was initially bolted with 6' resin bolts, trusses, had been added as secondary support. Cause was determined to be water & slip in the weakened roof.