Technology of weakening and danger-breaking dynamic disasters by hard roof

With the increasing of coal mining depth,the strong pressure dynamic disaster by hard roof intensify day by day,which seriously threatens the safety of mine production. Based on typical coal mine with the hard roof disaster of Shendong mining area,the verburden rock fracture under fully mechanized caving mining with hard roof are studied and the principle of dynamic hazards caused by dynamic overloading of static and dynamic loads due to “ cantilever beam” rotating collapse of low key layer is presented,the effectiveness of roof weakening to control the dynamic disas- ter of strong ore pressure is revealed,which are comprehensive using physical simulation,numerical analysis,technolo- gy development,the engineering application methods. Based on this,the control methods for preventing rock burst of multi-point drag hydraulic fracturing of rigid roof was proposed,the detection technology of fracturing influence range of directional long borehole ( >400 m) based on transient electromagnetic in borehole was developed,and its engineering application is carried out in typical mines. Three drilling holes are arranged in a single drilling field,the length of drilling holes is 330 -600 m,and the diameter of drilling holes is 96 mm. This fracturing has realized the effective weakening of the whole region in the 310 m working surface with a single hole over 600 m and 12 fracturing sections, and the cumulative water injection volume has reached 2 957. 25 m3 . The results show that the maximum hydraulic fracturing pressure is 30. 5 MPa,the maximum fracture pressure drop is 12. 90 MPa,and the pressure drop above 3． 0 MPa is more than 365 times by implementing the roof section hydraulic fracturing weakening technology accord- ing to the selected of fracturing target layer by determination formula. Eleven low-resistivity abnormal zones affected by fracturing were detected,and the impact range of fracturing was judged to be 35 m. The roof pressure step,dynamic factor,maximum pressure are respectively reduced by 18. 90% -70. 60% ,5. 79% -7. 90% ,13. 65% -19. 40% which are compared with the un-fractured sections,the deformation along the groove is effectively controlled. The dynamic disaster of hard roof is weakened and solved,the equipment and technical are providing for large area advance weake- ning in working face or panel.