| As an important reference for coal mine gas prediction,extraction and gas outburst prevention and control,the change of gas adsorption characteristics under the influence of external action is rarely reported.Therefore,this article through to the shock structure under the action of the opposite sex to study the influence of coal adsorption properties,low permeability,extraction in China is difficult to prevention and control of gas utilization of coal resources and has important engineering significance.As a consequence,this paper,which took No.3 coal seam coal body of No.2 Yangquan Mine,Shanxi as the research object,after using the improved vertical hopkinson bar(SHPB)pressure system to impact the coal structure the opposite sex,analysed the pore size structure and adsorption properties of coal samples before and after impact through low temperature liquid nitrogen adsorption experiments and methane isothermal adsorption experiments respectively.The following main conclusions were obtained.(1)The stress-strain curves of the coal samples were generally consistent after being impacted at different strengths in the vertical SHPB compression bar system,and were all upwardly convex elastic-plastic curves.With the increase of impact strength,the dynamic compressive strength of coal samples increased linearly.When the strain rates were similar,the dynamic compressive strength of the coal samples in the direction parallel to the laminae was always smaller than that of the coal samples in the direction perpendicular to the laminae,which was more sensitive to the impact effect.(2)In low temperature liquid nitrogen adsorption experiment,the adsorption and desorption curves of structurally anisotropic coal bodies were consistent before and after the impact of different strengths,and there was an obvious "hysteresis loop",all of which were type IV isotherms.With the increase of impact strength,the entrance and specific surface area of coal was a linear gradient.The impact effect had little effect on the specific surface area ratio of pore diameter at each stage of coal sample,including the surface area of the micropores account for between 42% and 50% of the total surface area of the pore size,which was the main contributor to the surface area of the coal samples,and the surface area of the mesopores account for the smallest of the three pore sizes between 22% and 28%.(3)In the methane isotherm adsorption experiment,the Langmuir model was used to fit the methane adsorption curves of coal samples before and after impact,and the fitting degrees were all above 0.99.The inflection points of the adsorption curves occurred between 2 MPa and 3 MPa.The relationship between the adsorption constant a and the impact strength of the coal samples was linearly decreasing and the adsorption constant a of the coal samples in the direction perpendicular to the laminae was always greater than that in the direction parallel to the laminae at the same impact strength,while the impact force and impact direction had little effect on the value of adsorption constant b.(4)The specific surface area of coal sample directly affected the adsorption quantity of coal samples of methane.Under the impact,the coal sample micro aperture structure changed,and specific surface area decreased with the increase of impact strength,and then coal samples of methane adsorption quantity was less.It was well confirmed the change of microscopic pore size structure of structurally anisotropic coal bodies by the impact effect from a macroscopic perspective. |
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