Analysis on hazard characteristics of overburden structure in steeply inclined coal seam

Aiming at the problem of dynamic hazard caused by roof impact instability in goaf of steeply inclined coal seam in Urumqi mining area,according to the geological conditions of Wudong Coal Mine,the cause of the hazard was analyzed,and a mechanical model of overburden structure in steeply inclined coal seam is established. Combined with the characteristics of roof energy distribution,the source of hazard is clarified,and prevention and control measures are put forward. Meanwhile,the physical similarity simulation test of hazard caused by over-burden structure is designed, the temperature and acoustic emission (AE) parameters were recorded with the infrared thermal instruments and AE sensors,and the discrete element numerical calculation is used to obtain the spatiotemporal information of the hazard source to guide the prevention and control of dynamic hazard. The results show that the “arch-beam” structure formed by roof rock beam and overburden stress arch in steeply inclined coal seam has the characteristics of spatial structure correlation,and the instability of this structure induces dynamic hazard under the condition of high stage horizontal sectional short wall fully mechanized top coal caving mining. Also,the energy distribution of the roof rock beam can be divided into three zones: shoulder angle initiation zone, separated evolution zone and high energy compression zone,among which the high energy compression zone is the key hazard causing area. Furthermore,the dynamic fracture of overburden structure has the characteristics of periodic temperature and AE parameters,combined with the evolu- tion characteristics of average infrared radiation temperature and AE energy rate in the three zones,the roof failure pe- riod can be divided into low level development,pre-earthquake calm,accelerated active and relaxation stages,in which the accelerated active stage is the hazard preparation stage. Based on the research results,the pre-cracking measures of goaf roof are formulated,the effect of borehole television is obvious,and the hazard is effectively controlled,which pro- vides a reference for the prevention and control of dynamic hazard in steeply inclined coal seam mining.