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Applying the theory of cylindrical cavity expansion, the mechanical characteristics of gas-filled coal were studied. Expressions of stress distribution were expressed in cavity expansion zone, fractured zone, plastic zone and elastic zone. The mechanism of cracks evolution in coal was investigated based on theoretical expressions, numerical simulation and model experiment. The results show that the interaction of compression wave and unloading wave form cracks in gas-filled coal. The main energy of blasting is used to form fractured zone, so the coal have more lager area than rock under blasting loads. [ABSTRACT FROM AUTHOR]

In order to search for the gas distribution in the coal seam after hydraulic flushing, introduced a hydraulic flushing field test on the investigation of gas pressure based on Pansan No. 13-1 coal seam occurrence condition. By using RFPA2D-Flow software to simulate the process of coal fracture with hydraulic flushing, studied the effects of hydraulic flushing in seam stress and gas pressure distribution. The results indicate that hydraulic flushing pressure-relief and permeability is a process of the coal around punching holes and rebuild its unstable equilibrium. Around the holes from near and far would form four regions: gas full emission region, gas emission region, gas pressure transition region and natural gas region. The coal in the pressure-relief and permeability region could experience the processes of stress increase, fracture development, stress quick release and recovery equilibrium. [ABSTRACT FROM AUTHOR]