The failure of top coal plays an important role in the successful sub-level mining, and also it is vital to coal bump. By using RFPA2D (Rock Failure Process Analysis), the extremely thick coal seam is investigated in this paper. The extremely thick coal seam locates at the 21121 working face (fully mechanized sub-level caving longwall working face) of Qianqiu Mine, Yima Coal Mining Administration. The results keep good agreements with the consequence from the deep-hole base station in-situ displacement measurement. More important, it can be seen from RFPA2D simulations that the advancing abutment distance of 21121 working face is much longer, and that the interval of top coal can generate apparent abscission layers. The obvious periodicity and beams rotation of top roofs also play a more important role in the fragmentation of the extremely thick top coal. On the basis of these characteristic analysis, the advancing abutment zone of 21121 working face with the maximum scope of 90m 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. Such dividing can do great benefit to the safety and high efficient mining of the extremely thick coal seams.
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