Study on Pre-Cracking Technology of Mine Roof in Fully Mechanized Top Coal Caving Mining Face

Due to a high thickness dense and hard of the main roof could not be easy falling during the mining process,a large area suspended roof could be easily formed. In order to reduce the suspended roof area,reduce the initial falling distance of the roof,prevent or reduce the gas content over limit in the upper corner of the coal mining face,and prevent the roof falling and large area top coal falling during the initial mining period to cause the gas content over limit in the coal mining face,a weakening treatment of the roof would be necessarily conducted. According to the geological and mining conditions of No. 1311 coal mining face and the overburden strata structure features,a roof pre-cracking blasting plan and the related technical parameters were determined. The practice results showed that the blasting borehole drilling in the open-off cut should be conducted with a group as a unit. With the optimization of the blasting plan,the bottoms of the blasting boreholes were evenly distributed in a straight line. The site observation and analysis on the roof weighting indexes showed that the pre-cracking blasting of the roof could effectively weaken the initial roof weighting intensity and realize the safety mining.