Mining Fracture and Porosity Distribution of Overlying Oil Shale in Coal Mine Stope
In order to study the evolution mechanism of mining fractures in overburden during the advancement of overlying oil shale working face,taking Nanjiazui Coal Mine in Zichang County as the engineering background,the UDEC simulation software was used to analyze the caving characteristics of overburden and the dynamic evolution law of stress relief zone,and the three-dimensional porosity distribution law of caving rock mass under full mining was obtained according to the subsidence of rock stratum.The research shows that the caving form of overburden in the stope is as trapezoidal distribution with narrow upper part and wide lower part,and the mining fractures are stably developed on both sides of the goaf,and the middle part is gradually compacted to the minimum value.The vertical stress of the pressure relief zone is significantly lower than that in the middle of the goaf,which occurs in the oil shale of the stope collapse zone.The distribution pattern of the pressure relief zone gradually changes from"V"shape to"W"shape with the advance of the working face.According to the three-dimensional porosity distribution model of the caving rock mass in the goaf,it can be seen that the high porosity area in the same level is circularly distributed,and the circular area gradually shrinks to the middle of the goaf with the increase of the height of the rock layer,and the whole structure is as hollow terrace.
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