Investigation of Pore Structure and Adsorption/Desorption Properties of Coal in the Non-uniform Stress Zone: Implications for Coal and Gas Outburst.

The haulage roadway of the F₁₅-22080 working face, No.8 mine is situated within a special non-uniform stress zone. In this area, the extraction-boreholes drilling process frequently triggers coal and gas outburst. Against this background, this study systematically conducted high-pressure gas adsorption experiments and high-pressure gas desorption experiments on coal samples collected from different stress zones and obtained their adsorption/desorption characteristics. Subsequently, coal pore structure characteristics at various scales were investigated by employing scanning electron microscopy, low-pressure N₂ adsorption and low-pressure CO₂ adsorption techniques and fractal analysis to assess the impact of varying stress levels. On this basis, a comprehensive analysis was carried out to explore the connections between stress, pore structure, adsorption/desorption traits, and the risk of outburst. The results indicate that, with increasing stress, the Protodyakonov coefficient f and the Langmuir pressure P_L decrease, while the index of diffusion initial velocity of coal gas Δp and the Langmuir volume V_L increase. The desorption amount and rate of gas also increase significantly. The total pore volume and specific surface area of micropores increase, while those of mesopores and macropores show an overall decreasing trend. The surface fractal dimension D_F1 increases by 9%, the spatial fractal dimension D_F2 decreases by 5.2%, and the volume fractal dimension D_SIE increases by 1%. The induced stress leads to a decrease in the abundance of macropores and mesopores, with concurrent increase in micropores. The V_L exhibits a linear increase with the D_SIE, whereas the P_L demonstrates a linear decrease with it. The initial desorption rate rises with the reduction of the D_F2 and the increase of the D_SIE. The influence of superimposed-stress on outburst stems from alterations in pore structure and adsorption–desorption capabilities. Simultaneously, it collectively heightened the outburst risk by increasing the gas pressure gradient and weakening the strength of the coal. [ABSTRACT FROM AUTHOR]