Experimental study on permeability properties of stratum medium of Xiaojihan coal mine and genetic mechanism of the coal seam becoming a main aquifer

Based on Yulin-Hengshan coal field in northern Shaanxi of the special geological background,the permea- ting mechanical properties of coal-bearing strata in Xiaojihan Coal Mine were studied by transient permeation tests in this paper. According to the collected time series of pore pressure at both ends of the rock samples,the authors ob- tained the time series of seepage velocity and its change rate by the difference method,and then by the least squares method,the authors calculated and obtained the permeability,non-Darcy flow coefficient and the acceleration factor during the total stress and strain process of the rock samples from different strata under different confined pressures, and the authors compared the maximum and minimum permeability of different strata. The research results are as fol- lows:① with the increase in compression strain,the stress peak of coal samples lags its permeability peak;② during the stage after the peak stress,the non-Darcy seepage factor and acceleration coefficient of coal samples firstly increase dramatically and then decrease significantly,both these two peak values lag the stress peak;③ the highest permeability of the destructed samples from the Luohe group Medium-grained feldspar sandstone and the No. 2 coal stratum are significantly higher than that of the other rock strata;④ the permeability of the destructed coal samples achieve 1×10-15 m2 magnitude,which is much higher than that of coal seam from the other coal mines;⑤ the sandy mudstone in Fuxian group has the lowest permeability in all strata and it can be considered as a water resisting layer.