Research on Directional Hydraulic Coal Cutting and Outburst Prevention Technology in Soft and Hard Composite Coal Seams

Affected by tectonics, soft and hard composite coal seamsare widelydistributed in China; the soft stratification in the soft and hardcomposite coal seam is the key to controlling the occurrence of coaland gas outburst accidents. Based on this, for soft and hard compositecoal seams, in order to accurately extract soft layers, a directionalhydraulic coal mining equipment has been developed, including a drillingrig pump truck system, a directional coal wireless measurement system,and a cutter drill pipe system. By constructing a mathematical modeland conducting numerical simulations, it was found that the verticalstress, horizontal stress, and gas pressure of the coal body aroundthe borehole after coal extraction decreased significantly comparedto normal borehole conditions; the on-site test results indicate thatthe hydraulic coal extraction volume of directional hydraulic coalextraction boreholes reaches 0.25 m(3) per meter. The totalamount of coal extracted accounts for more than 3 & PTSTHOUSND; of the totalamount of coal within the coverage area. The average concentrationof gas extraction in the coal extraction area is 80.15%, and the netamount of gas extraction from 100 m boreholes reaches 0.17 m(3)/(min & BULL;hm). After extraction, the measured residual gas contentin the coal extraction and non-extraction areas decreased by 59.27and 40.38%, respectively. Directional hydraulic coal mining technologycan effectively solve the problem of coal and gas outburst preventionin soft and hard composite coal seams and has good application prospects.