Change law of permeability of coal under temperature impact and the mechanism of increasing permeability

To study the change law of permeability of coal under the condition of temperature impact and the mecha- nism of increasing permeability,the temperature impact test of two kinds of conditions of coal samples were carried out using thermostat and liquid nitrogen,the permeability variation of coal samples before and after temperature shock and the development of micro fracture were analyzed,and the distribution of acoustic emission signal in the process of tem- perature shock was also discussed. The experimental results indicate that after the cold shock treatment and hot-cold shock treatment,an average increase of permeability of coal were 48． 68% and 469． 24% respectively,the AE energy peak during hot-cold impact process is 3． 6 times of that during the cold shock process. Compared with cold shock treatment,the hot-cold impact process produces more number of crack,the fractures show a dendritic development,and the effect of increasing permeability is better. The thermal stress exceeding the tensile strength of coal produced by the anisotropy and thermal shock properties of coal is the main mechanism of increasing permeability.