Relieving Pressure and Improving Permeability of Soft Coal at Top and Bottom by Hydraulic Cavitation

For enhancing the effect of gas extraction, applying Wuyang Coal Mine in China as the engineering background, the technology of hydraulic cavitation at the top and bottom of soft coal (HCTBSC) with low permeability was put forward. FLAC3D was utilized to build the calculation model, and Tecplot was employed to process data of the results, revealing the characteristics of stress variation in coal seam for different cavitation radius and different distribution forms of cavitation. The field test scheme of HCTBSC was determined to verify the simulation results. Results show that the effectiveness of stress relief (ESR) is controlled by the cavitation radius and cavitation distribution forms. The dimension of pressure relief emanates via the cavitation elongating outward with the cavitation radius, and the stress changes in the coal are different due to different cavitation distribution forms. The field test proves that the technology of HCTBSC is more effective in relieving pressure, increasing the productiveness of gas extraction, and decreasing the scourge of coal and gas protrusion. The obtained conclusions in this study provide guidance for the hydraulic cavitation application in soft coal.