Experiments study on effects of loading and unloading rates on damage-permeability aging characteristics of gas-bearing coal

For exploring the effects of the loading and unloading rates on the damage-permeability aging characteristics of gas-bearing coal,the damage-permeability experiments for gassy coal were performed with the different loading and unloading rates by the experimental equipment for coupling adsorption-seepage-mechanic properties in the paper.The results show that the higher the axial loading rate or confining pressure unloading rate is,the faster the time response of the coal damage is and the slightly lower the peak strength of coal is;that is,the loading and unloading rates significantly affect the aging characteristics of coal damage,but have less effects on the ability of coal to resist failure.The coal samples are damaged steadily with the lower loading and unloading rates while the coal samples are damaged and destroyed acutely with the higher loading and unloading rates.The higher the loading and unloading rates are,the faster the time response to the permeability is and the larger permeability increase is;the post-strength permeability of the coal with the conditions of decreasing confining pressure and fixing axial loads can reach 163.0%～206.3% of the original permeability.The effect of confining pressure unloading on the damage-permeability characteristics of mining coal mass is much greater than that of axial loading and thus the coal mining speed should be properly controlled for avoiding the coal-rock gas dynamic hazards in the engineering practices.