Laws of sub-level coal's failure and displacement in extremely thick coal seam's sub-level caving mining face

By using of RFPA2D, extremely thick coal seam mined in fully mechanized sub-level caving longwall working face of Qianqiu Mine, Yima Coal Mining Administration, is studied in detail. The results accord with theory calculation. What's important, it can be seemed from RFPA2D simulation experiments that advancing abutment zone of 21121 working face is longer, and that the interval of top coal can generate apparent abscission layers and the top coal's failure has a obvious periodicity and beams rotation of roof play a more important role in extremely thick top coal's fragmentation. On the basis of analysis of these characters, the advancing abutment zone of 21121 working face with the maximum scope of 90 m is divided into the following micro-zones: initial compression and plastic deformation zone, strong compression and damage zone, roofs rotation action and supports action zone, which can do great benefit to extremely thick coal seams' safe and high efficient mining.