Experimental Study On Cracks Evolution And Permeability Of Coal Sample Under Cyclic Loading

Coal is dual media of fracture and pore,and its pore is the main place of gas storage,fracture is the main channel of gas flow.The double medium property of coal determines its permeability has high stress sensitivity.The change of loading state of the coal causes the change of the pore structure,and then affects its permeability.In the field of mining engineering,coal is often subjected to cyclic loading,the pore fissure structure within coal is in dynamic change,which will influence the gas flow in the coal body,resulting in uneven gas emission,gas concentration overrun,gas outburst and other major disasters,caused a huge threat to the safety of coal mine production.Therefore,research for the cracks evolution process and permeability variation low of coal under cyclic loading have great significance for the prevention of gas dynamic disaster.Firstly,this paper carried out mechanical and acoustic emission experiments of coal samples under cyclic loading,under different stress levels and cyclic frequencies,the deformation curves and acoustic emission parameters have experienced three stages: the stress-strain curves show sparse-dense-sparse,peak ringing count,increase rate of cumulate energy and impact counts are presented to reduce-stability-rising trend.Secondly,permeability experiment of coal samples were conducted,the results showed that: with the increase of cycle numbers,permeability showed the trend of reduce-stability-rising,in the stage of permeability reduction,the relationship between permeability and cycle numbers is power function,in the stage of permeability increase,the relationship between permeability and cycle numbers is exponential.Finally,the paper analyzed the relationship between deformation and acoustic emission parameters,deformation and permeability,and based on the deformation,the relationship between acoustic emission parameters and permeability is qualitatively analyzed,it is concluded that: in the circulation process,the permeability of coal samples in the max stress point has the same change trend with peak ringing count,and the growth rate of cumulate energy and the impact counts is proportional to the count.