Research on the instability mechanism of the roof structure and hydraulic fracturing control technology in longwall recovery room

Pre-driven longwall recovery room suffers excessive mining pressure and is vulnerable to roof instability.In this paper,a mechanical model of the key block of the advance fracture of the main roof was established,and the effects of different weighting positions and hanging roof structures on the stability of longwall recovery room were compared and analyzed.The results show that reducing the length of the hanging roof behind the support and the extrusion force between rock blocks and improving supporting intensity can reduce the force of unstable roof rock blocks on the support.The rotation and subsidence of the key block will cause serious damage to the surrounding rock when the fracture position of the main roof is close to the upper part of the recovery room.Hydraulic fracturing can promote the breaking and subsidence of the roof strata,reduce the intensity of weighting at the end of the mining period or even change the law of weighting so that the surrounding rock of the recovery room can be protected from the strong mining pressures.The field application showed that the support resistance and surrounding rock deformation were significantly reduced due to hydraulic fracturing,which realized the safe and efficient removal of the 31108 working face of the Huoluowan colliery.