Research On The Effect Of Outburst Prevention In Mining The Lower Protective Layer Of Honglin Coal Mine In Guizhou Provinc

Due to the unstable occurrence of coal seams and complex geological conditions in Guizhou Province,coal and gas outburst accidents occur frequently.In the ten years from 2011 to 2020,there were 27 outstanding accidents in coal mines in Guizhou Province,with 247 deaths.A large number of practical experience shows that the protective layer mining can greatly enhance the permeability of coal seam,reduce the difficulty of extraction,improve the gas extraction rate,and fundamentally eliminate the risk of coal and gas outburst.Based on the practice background of Honglin Coal Mine in Guizhou Province,this paper studies the outburst prevention and protection effect of lower protective layer mining.By using the methods of theoretical analysis,numerical simulation and field test,the mining process of the lower protective layer is analyzed,the outburst prevention mechanism of the lower protective layer mining is studied,and the effect of pressure relief and outburst prevention of the lower protective layer mining is verified.The main results are as follows:（1）Through the analysis of the failure and deformation of the overlying coal strata after the mining of the lower protective layer,the migration and distribution laws of the overlying coal strata under the influence of mining are obtained.（2）Through the geological condition investigation of Honglin coal mine,the theoretical pressure relief range of lower protective layer mining is calculated.（3）Using FLAC^3Dnumerical simulation software,the numerical simulation model of the lower protective layer mining in Honglin Coal Mine is established,and the evolution law of the plastic zone and the change law of stress and displacement of the top and bottom coal strata are analyzed.After the end of mining face advancing,the plastic zone presents symmetrical distribution with the central axis of the working face,and the shape is similar to the butterfly shape.In the process of advancing the mining face,the stress distribution shows the rule of concentration in the middle of the mining face and reduction at both ends.The influence range of mining face on the displacement change of overlying coal strata is significantly greater than that of the strata below.The distribution of roof displacement after excavation is similar to the’V’distribution,which has a certain symmetry.（4）Through the analysis of field drilling test data,after the mining of protective layer,the gas content of No.9,No.12,No.13 and No.14 coal seams was greatly reduced,with an average decrease of more than 70%.The gas pressure of No.9 coal seam was reduced by 67.5%,and the gas content of coal seam was reduced by75.5%.（5）Through the field measurement of the protection range,it is determined that the measured protection range is greater than the theoretical pressure relief range,and the pressure relief effect of the lower protective layer mining is up to standard.