Research On Mechanism Of Enhanced Gas Permeability Of Coal And Rock Under Various Mining Layouts

The mining-incuced mechanical behavior of coal and rock including mechanism on propagationand connectivity of cracks is the theoretical basis of the enhanced coalbed methane recovery, asalso as a key technical support for simultaneous exploitation of coal and gas in deep coal mining.Based on three typical mining layouts including the non-pillar mining, the top-coal caving and theprotective coal mining, the coupling test research between stress and gas permeability have beencarried out. By establishing the optimization of mechanical model considering crack defects, themining-induced mechanical behavior of coal in the front of working face and the quantitativedistribution of the mining state of stress with gas permeability characteristics are obtained. Thequantitative evaluation studies are successfully carried out about the pressure relief-inducedenhancement of permeability under protective coal mining by creatively introducing probabilityintegration method to the relationship between volumetric strain and permeability. Based onpermeability test coupling the stress, the visualization technology is proposed to capturepermeability distribution of whole mining field in the similar simulation experiment，and themathematical equation between volumetric strain and gas permeability is obtained to evaluate theeffect on enhancement. Furthermore, the breakthrough of the new methods including the areacovering method to calculate the fractal dimension of crack curve in the three-dimensional spaceand the volume covering method to calculate to the fractal dimension of rough surface are putforward to solve the problem of accuracy and flexibility in the calculation of the fractal dimension, which could be an effective method to study the fractal influence on permeability ofthree-dimensional cracks and fracture surface in coal.