Study on the permeability of overlying aquifer associated with the mining of the super-thick coal seam in Dajing mining area of eastern Junggar coalfield

Based on the deposition of overlying rocks and their properties, the authors establish the physical model and the consequent numerical model.With these two models, the simulation of overlying rocks movement and the permeable characteristics of aquifers are investigated.The results show that the displacement of referring points from the physical similar experiment has the same change as that from numerical simulation for the mining of the first sub-layer of the super-thick coal seam in eastern Junggar coalfield.During mining of the first sub-layer, the displacement of reference point 1^# increases quickly from the mining period of 70-250 m for physical experiment and 100-300 m for numerical simulation respectively, then stays stable.The displacement of reference point 2^# increases quickly from the mining period of 70-420 m for physical experiment and 250-500 m for numerical simulation.And the displacement of reference point 3^# increases quickly from the mining period of 430-600 m for physical experiment and 450-600 m for numerical simulation.For the porous medium, a negative correlation exists between the permeability and the effective stress for each reference point of overlying aquifer.For the fracture, a positive correlation exists between the fracture permeability and the effective stress for each reference point of overlying aquifer.Further simulation shows that the values of permeability with reference points present an order as 1^#> 3^#> 2^# during the stage of mining No.1 sub-layer to No.5 sub-layer one by one.Meanwhile, the values of permeability of reference points also demonstrate an order as 3^#> 1^#> 2^#.From this study, it's obvious that a coupling effect exist among the effective stress, the porous permeability and the fracture permeability of aquifers.