Numerical simulation of evolution rule of cracks in surface goaf gas drainage hole

In order to ascertain the reason of gas enrichment in the goaf of T2291 working face and the flowing channels of gas, the features of mining caused fractures of overlaying strata of T2291 in Tangshan coal mine is studied in this paper by using FLAC3 D and UDEC software. The common nature of stratum movement and the development procedure of crack are described; distribution characteristics of O-type circle fracture in the top floor mining along the strike are verified. The results showed by numerical simulation that the connecting fracture under the adjacent goaf is affected by the isolated coal pillar width and under the condition of hard roof the crack along the strike emerges saddle-backed state. The fundamental reason of longlasting drainage is that more goaf in lateral and longitudinal direction is connected by the crack in T2291 drilling.