1.Coal Mining and Design Department, Tiandi Science and Technology Co.,Ltd.,Beijing ,China;2.State Key Laboratory of Coal Mining and Clean Utilization, Beijing ,China

It is difficult for the hard roof to fall down in time, resulting in strong mining pressure on the working face, severe deformation of the roadway and difficult management. The No.5209 auxiliary transportation roadway of Madaotou Coal Mine was taken as the engineering background. Through on-site investigation, theoretical analysis and surrounding rock, geological mechanics parameter test, industrial test and other means, a set of technologies were put forward based on single-hole segmental multiple fracturing as the core of hard roof with extra-thick coal seam and hydraulic pressure fracturing and top-loading roof under strong dynamic pressure, including drilling arrangements, fracturing parameters, fracturing equipment and fracturing processes. On-site test of single-row and double-row hydraulic fracturing and top-cutting pressure relief was carried out in different sections of No.5209 auxiliary transportation roadway. The pre-stress relief of the working face was dominated by the L-hole of the coal pillar, the S-hole pressure relief borehole on mining side was added 100 m in advance of the final mining face and field test and monitoring were carried out there. The fracturing test shows that the maximum cracking pressure of K3 coarse sandstone exceeds 50 MPa, and the pressure is 15～30 MPa. The effect of water in the adjacent observation hole during fracturing is good, and it can realize layered pre-splitting for hard and difficult roof. The monitoring data of mine pressure shows that after the hydraulic fracturing and topping pressure relief, the deformation of the dynamic pressure roadway is significantly reduced, the deformation of the roadway is reduced by 70%, the working resistance of the end support is reduced by 35%, and the impact distance of the working face is reduced from 70 m to within 30 m. The successful implementation of the research results in the field engineering practice provides a reference for the promotion and application of the hydraulic fracturing and topping pressure relief technology in the mining of the hard roof of the extra-thick coal seam.

天地科技股份有限公司科技创新创业资金专项资助项目（2019-TD-QN002）；国家自然科学基金资助项目（51774186）；开采设计事业部“科技创新基金”资助项目（KJ-2018-TDKCZL-12）