Disaster mechanism during passing of working face under overlying remnant coal pillar and advanced regional prevention technology

When the mining of the underlying working face of shallow and close seam passes under the overlying remnant coal pillar, it is easy to have an intensive mine pressure-induced dynamic disaster, resulting in personnel and equipment damage, which seriously threatens the safety of mine production. The characteristics induction, numerical simulation calculation, mechanical model analysis and other research methods are used to clarify the occurrence of the hazards of the overlying remnant coal pillars in the shallow and close seams, and reveal the disaster mechanism caused by intensive mining pressure. The research shows that the disaster mechanism of the intensive ground pressure caused by the overlying remnant coal pillar is that when the working face passes under the coal pillar, the coal pillar and the overlying bearing body are disturbed and suddenly lose stability, and the energy is transferred to the stope instantly, which is released in the form of kinetic energy, resulting in the intensive ground pressure-induced dynamic disaster. Based on the prevention and control idea of “collapsed rock support+weakening of key rock stratum+transfer of stress transmission path”, the prevention and control technology of weakening for front area using subsectional-hydraulic fracturing was proposed by modifying the coal pillar and bearing body migration space, weakening key rock stratum, uniformly distributing concentrated stress and transferring stress transmission path, and engineering tests are carried out at typical working faces. The engineering test results show that during the implementation of hydraulic fracturing, the peak value of pumping pressure reaches 23.4 MPa, the pressure changes generally in a “zigzag” shape, accompanied by a sudden drop of pressure for more than 60 times, and the artificial main fractures and micro fractures in the rock mass continue to develop alternately, effectively destroying the integrity of the rock mass; After treatment, the peak value and average value of periodic pressure decreased by 15.41% and 8.29% respectively, and the peak value and average dynamic load coefficient decreased by 17.39% and 11.88%, respectively. The maximum contraction of the shield cylinder was 50.00% and less than 0.4 m, and the maximum contraction of the gate road roof was 33.33%. The working face safely passed through the affected area of the overlying remnant coal pillar, and the advanced area weakening technology of subsectional- hydraulic fracturing can effectively prevent and control the intensive ground pressure disaster of the overlying remnant coal pillar in shallow and close seams.