Multi-dimensional hydraulic fracturing technology for thick and hard top coal to increase caving

Aiming at the problem of poor top coal caving performance during top coal caving mining in thick and hard coal seams, the process law of advanced hydraulic fracturing combined with hydraulic fracturing between hydraulic supports is studied through field tests.The results show that the peak pressure of advanced hydraulic fracturing is 14-20 MPa, and the total fracturing time is 74-138 minutes.Hole H1 and hole H3 have longer fracturing duration and higher pressure peaks than hole H2.The peak pressure of hydraulic fracturing between hydraulic supports is 18-22 MPa, and the total fracturing time is 15-27 minutes.The peak water pressure at the upper end is higher than that at the lower end, and the fracturing lasts longer.The advanced hydraulic fracturing hole is deeper, the control range is large, the fracturing time is long, but the pressure peak is low.The hydraulic fracturing holes between the hydraulic supports are shallow, the control range is small, the fracturing time is short, but the pressure peak is high.The average water injection rate of advanced hydraulic fracturing holes is about 5 times that of hydraulic fracturing holes between hydraulic supports.The coal caving height during the stable period of hydraulic fracturing at the test working face increased by 82% compared with the area without hydraulic fracturing, which is close to the optimal mining and caving ratio.