Collapse filling-based technology of weakening and danger-solving by staged fracturing in hard roof

The working face is easy to induce dynamic disasters such as rock burst, coal and gas outburst, mine earthquake and hurricane in goaf under the condition of hard roof, which seriously threatens the safety of mine production. the pre-weakening and risk-solving technology of staged fracturing in hard roof is proposed based on the mode of advanced weakening by staged fracturing through open holes, combined with the synergetic support concept with "fracturing collapse body+coal pillar+load-bearing rock layer". By using the methods of theoretical analysis, technical research and development and engineering application, the crisis mechanism of advanced weakening of the staged fracturing in roof was explored, and the quantitative judgment formula for the formation of stable collaborative support system was developed, and the engineering application was carried out in Baode Coal Mine in Hedong Coalfield. The results show that the maximum hydraulic fracturing pressure is 22.43 MPa, the maximum fracture pressure drop is 6.17 MPa, and the pressure drop above 3.0 MPa is more than 167 times in three boreholes by implementing the hydraulic fracturing weakening technology of roof section according to the selected of fracturing target layer by determination formula. Through the analysis of the working face pressure before and after fracturing, the roof weighting step distance, dynamic load coefficient and average pressure after fracturing are reduced by 35.02%, 14.29% and 13.87% respectively, and the deformation along the roadways is effectively controlled. It is verified that staged fracturing can form artificial cooperative support system, realize the weakening and solution of dynamic disasters of hard roof, and provide technical and equipment support for the prevention and control of strong mine pressure disasters of roof under similar geological conditions.