The Study Of Caving Of Overburden Rock And The Distribution Law Of Porosity In The Goaf

Goaf is a porous media regional formed by the residual coal and broken rock, its internal gas flow field distribution is mainly affected by porosity and permeability of goaf, and porosity and permeability is determined by the caving subsidence law of overburden rock. Therefore, analyze the caving law and three-dimensional porosity distribution rule of the overburden rock with mining, has the important guiding significance in the research of distribution law of flow field in goaf.The research background of this paper is the general geology of Wangzhuang coal mine, combine with the rock mass quality classification, calculate that joint spacing and rock mass mechanical parameters of each strata. Using the CDEM software to simulate the 8101 working face, determine the distribution range of goaf "vertical three zones" :the range of caving zone is about 0~25m; and the range of the fractured zone is about25~65m, and compare the simulation result with the calculation results by empirical formula and investigation results by the high level borehole. The comparison result of our investigation shows that the numerical simulation is more tally with the investigation of actual situation, the study verifies the rationality of joint spacing and rock mass mechanical parameters.Establish the three-dimensional physical model according to the actual situation of goaf, then this paper simulate the movement of overburden strata under the mining conditions of three-dimensional space, then we take the different profiles along the trend and tendency of the working face in the model,and analyze the breaking and caving law of the overburden: with gradual promotion of the working face, the overlying strata began to rupture, when the working face is advanced 500 m, the subsidence of strata have been basically stable, reach the maximum, the subsidence of strata increased with the increase of the distance from the working face and coal wall;near the working face and coal wall, due to the strutted influence of the coal wall, the subsidence is obviously reduced; Along the vertical direction of goaf, the strata subsidence is decreased from the bottom up.Combine with the subsidence of the strata, calculate that expression of porosity in goaf, and then we fit distribution map of the porosity in three-dimensional space by theMATLAB software, the results showed that: Along the trend direction of goaf, the is reduced with the increase of the distance from the working face, the maximum can reach 0.3, when the distance is more than 100 m, the porosity keeps invariant; Along the vertical direction of goaf, the porosity is decreased from the bottom up,but when it is far from the working face and coal wall, the porosity in caving zone is smaller than that in fractured zone. Then we apply the expression of porosity to the Fluent software, the distribution law of flow field in goaf is simulated, compare the numerical simulation results of the gas concentration in the upper corner and pressure difference of working face with the field test data, verifies the rationality of the goaf porosity which is calculated by numerical simulation, As the same time, the study also provides theoretical basis for further research on the distribution law of flow field in goaf.