Application of deep borehole pre-cracking blasting to coal mining in high gassy and ultra thick seam

According to the high value gas emission and low gas drainage rate during the coal mining operation in high gassy and low per- meability ultra thick seam,a measure of deep borehole pre-cracking blasting and gas pre-drainage was conducted.The paper studied the borehole drilling technical parameters influenced to the low permeability ultra thick seam.The test results showed that with a special gate- way for the blasting operation,a fan type borehole pattern drilling and the explosives loading and blasting were conducted in the coal wall and under the blasting pressure,cracking and pressure releasing were occurred in the seam and the broken ring,pressure releasing ring and fissure ring were formed along with the boreholes in the seam from the inner to the outer of the seam.Thus,the permeability coeffi- cient of the seam increased and the gas drainage rate of the low permeability ultra thick seam increased.With the deep borehole pre-crack- ing blasting and gas pre-drainage measures for No.215 fully mechanized top coal caving mining face in Xiashijie Mine of Tongchuan,the gas drainage rate of the coal mining face increased over 10% and the safety dangers during the face coal mining period was reduced,which could be guidance to gas control in the future.