Instability mechanism analysis and reinforcement technology of gas drainage drilling soft-broken coal seam

In order to solve the problems of the borehole sealing quality is poor and borehole instability is prone to occur under the disturbance from mining activities during the gas draining process,this paper takes No.13 coal mine of Pingdingshan as the research engineering background,based on the mechanism analysis of borehole instability and deformation,this paper propose a novel technology to improve the borehole stability,which is combined curing the front-end coal of the borehole by high-strength cement mortar with the installation of screen pipes into the borehole to provide active support. The novel technology is applied on the mining face of F15-17—11030,and the industrial test results show that the testing borehole decay much more slowly and the drainage service life much longer than the conventional borehole. The maximum gas drainage concentration of testing borehole is approximately 1.3 times that of the conventional contrast borehole. Around the 10th day,the conventional contrast borehole occurre to be instability failure,the gas drainage concentration and negative pressure of suction around borehole front-end both dropped abruptly. However,the applied the technology testing borehole kept high efficiency gas drainage. Relying on the support from the screen pipe,could improve the physical and mechanical parameters of coal,making the broken the coal mesh with each other to keep the coal in suit preventing collapse and thus the stability of the borehole is improved,keeping the long-term stability of drilling and efficient gas extraction.