Research On Roof Controlling Techniques In45°horizontal Section Top-coal Caving

Full-mechanized caving mining in45°horizontal section top-coal caving not only hasthe problems that exist in the mining process of other coal condition, but also has it’s uniqueobstacles. The roof of the mined-out area is so difficult for caving, that it will hang inlarge-scale area. In the process of coal mining abrupt caving of the hanging roof oftenoccurred, it will result in rock burst, sudden overflow of poisonous gases and other disastrousaccidents, which would seriously restrict safety of coal mine. Therefore, the research on roofcontrolling techniques in45°horizontal section top-coal caving is significant.Based on basic geological and mining settings, western working face of+620meters innorthern panel, Wudong coal district of Shenhua Xinjiang energy co., ltd, hybrid analysesincluding theoretical analysis, in-situ engineering research and numerical simulation modelwere applied for revealing strata movement mechanism of overlying roofs in underexcavation and the key factor of roof breakage. Stable arch structure would form after roofbreakage, angle at the bottom of the arch damage will lead to the destabilization of all archstructure.With fully understand of softening mechanism on water injection, damage of water byrock would be fallen into four types: absorption, hydration, wedging and dissolution effect.Physical simulation model was built up scientifically and experimental schemes ofsimulation model and comprehensive monitoring was optimal. Monitoring system for the roofwas established, including close shot photography system which monitored the roofdisplacement, acoustic emission system which collected rock breakage events in the processof water injection, infrared system which monitored velocity and position of water seepage.Monitoring results showed that roof breakage effect was obvious after water injection, upper strata was caving in a V shape and crack was straight through surface directly.Carried out water injection was carried out at the bottom angle of the arch, destructiveeffect by high pressure water injection to roof strata and the destruction of the bottom angle tostability of arch structure were verified. Geological radar and optical borehole camera systemwere adopted to analyze deformation of the roof during the water injection, the results showedthat the zones which have contained original fissure crack would be more broken afterhigh-pressure water injection. The condition on roof breakage has big difference after waterinjection. So water injection softening effect is obvious in-situ monitoring.