Advance Pre-Cracking Blasting Technology of Roof Coal for Fully Mechanized Top Coal Caving Mining in Steep Inclined Thick Seam

In the fully mechanized top coal caving mining in the steep inclined thick seam,the top coal could be caved only when the top coal was fully weakened.But there would be dangers in potential when the top coal advance pre-blasting weakening technique conducted.In order to have a safety and high efficient fully mechanized top coal caving mining,to rationally set up the pre-blasting technique parameters to improve the breaking of the top coal,based on the analysis on the site seam deposit environment and mining conditions,the numerical simulation and the borehole peep were applied to analyze the top coal stress distribution law and the top coal breaking degree after the pre-cracking blasting of the top coal conducted.The results showed that the blasting releasing range was 1.2 m,the raw of the blasting boreholes was 4.5～5.0 m,the joint crack network distribution and evolution could meet the S type distribution law,the permeability of the seam was improved and the strata pressure behavior of the coal mining face would not be serious.The advance support pressure distribution range would be forward to the coal mining face and the stress concentration zone range was obviously reduced to have a safety mining operation.