Mechanism of the instability of strata structure in far field for super-thick coal seam mining

To overcome the problems of sharp decrease of hydraulic support’s prop and even emerging support crush- ing disaster periodically when the fully-mechanized top coal caving mining method is applied for mining the Carbonif- erous super-thick coal seam in Datong mining area,the methods of theoretical analysis and field measurement were used to study the mechanism of the instability of strata structure in far field for super-thick coal seam mining. The hy- pothesis that the movement of the “triangle plate” structure in far field impacts the mine pressure in super-thick coal seam working faces was proposed,and the “triangle plate” structural mechanics model for far field key strata broken in the shape of “horizontal O-X” for super-thick coal seam mining was established. Combining the field measurement in Tongxin coalfield,the geometrical parameters for the broken blocks of “triangle plate” structure for far field key strata broken in the shape of “horizontal O-X” were predicted,and the influence of its strike length and rotation degree on the structural stability was analyzed. The results show that this structure was easy to break when a big strike length and a heavy rotation degree of “triangle plate” existed. The floor heave deformation behavior of advancing segments in tail- gate on the side of free face of 8202 working face,Tongxin coalfield,indicated the breakage rule for the “horizontal O- X” breakage of far-field key strata indirectly. Based on the influential mechanism of the “ triangle plate” structure in far field on the mine pressure in working faces,the precautions of presplitting the far field key strata in advance and mining quickly under the “triangle plate” structure were addressed. The research work can provide a reference to the safe and high-efficiency mining and strong mine pressure controlling of faces with large mining height in super-thick coal seams.