Study on energy consumption and seepage characteristics of coal containing gas under cyclic loading and unloading

Taking the 8# coal seam coal sample of Malan mine as the research object, the mining axial cyclic loading and unloading experiment under different confining pressures is carried out to study the seepage characteristics and energy damage characteristics of coal body.The results show that with the cyclic loading and unloading of axial stress, the σ₁-ε₁ curve presents a spiral rise, and an obvious hysteresis loop is formed between the unloading curve and the next loading curve.The permeability-strain curve gradually turns into an elongated “strip” curve and crosses at lower confining pressure.With the increase of loading and unloading times, the absolute recovery rate of permeability decreases, and the maximum reduction rate is about 20%.The larger the confining pressure, the more difficult it is to recover the permeability.With the increase of the upper limit stress of loading and unloading, the total energy, elastic energy and dissipated energy absorbed by the coal body in the loading and unloading process all increase with the increase of cycle times, and the damage variable of the coal body also increases, but the rate of increase is slow.At the stage from the end of cyclic loading and unloading to the yield point of coal, the permeability decreases logarithmically with the increase of damage until the lowest point of permeability is reached.At the stage from yield point to coal body failure, the rate of coal body damage variable increases rapidly, the permeability increases exponentially with the increase of damage, and the coal body begins to accelerate the failure.