Strata structure and its effect mechanism of large space stope for fully- mechanized sublevel caving mining of extremely thick coal seam

In order to overcome the problems,such as the emerging support crushing disaster,advance supported de- formation and severe destruction of roadway on gob side and some other strong strata behavior problems when the fully- mechanized sublevel caving mining method is applied for mining the Carboniferous No. 3-5 extremely thick coal seam with hard roof in Datong mining area,this study used the methods such as theoretical analysis,physical simulation and field measurement to develop an evolving model for strata structure of mining extremely thick coal seam in large space stope. The result shows that both the key stratum motion at near and far fields in fully-mechanized sublevel caving min- ing at extremely thick coal seam may exert an influence on strata behavior. The structure model for near field key stra- tum is “cantilever beam + voussoir beam” broken in the shape of “vertical O-X” while that of far field key stratum is “voussoir beam” broken in the shape of “horizontal O-X”. The key stratum structure at near field mainly affects sup- port pressure and its stability on the working face. In the key stratum structure at near field,the more key stratums that move in “cantilever beam”,the more harm will be done to the safety of the support. The key stratum structure at far field mainly exerts an influence on the deformation of roadway on gob side of the working face. The rotary motion of the broken block will produce radial extrusion on wall rock in roadway on gob side,which is the main reason for the floor heave of roadway. Accordingly,the hard roof control technology,based on the near and far field synergetic ally weaken which combines ground drilling fracturing with underground pre-splitting roof,is developed. This technology will effec- tively reduce the pressure transmission from the energy release of rock breaking to the structural instability of key stra- tum and mitigate the mine pressure intensity of fully-mechanized sublevel caving mining stope for mining the extremely thick coal seam.