Experimental study on influence factors in damage-permeability characteristics of loading and unloading coal

In the process of deep coal seam mining, multiple factors affect the coal body damage-permeability characteristics.In order to reveal the evolution law of coal mining damage-permeability characteristics, the coal damage-permeability experiments under three mechanical paths of fixed confining pressure and increased axial pressure (path 1), fixed axial pressure and decreased confining pressure (path 2), increased axial pressure and decreased confining pressure (path 3) were carried out under different engineering conditions.Then the influence of factors such as loading and unloading methods, axial pressure loading rate, confining pressure unloading rate, and confining pressure on coal damage-permeability characteristics were analyzed.The results show that the different loading and unloading methods significantly affect the degree of sample damage, whose order is: path 1 < path 2 < path 3.The compressive strength of samples is easier to achieve with an increased rate of loading and unloading, but the extent of damage and permeability increase along with it.With the increase of confining pressure, the time response of damage becomes slow and the ultimate recovery degree of permeability decreases.The damage and permeability characteristics of coal have significant confining pressure effects.The cumulative amount of energy changes with time in an exponential function, and the relative permeability k/k₀ after damage expansion is in a power function.