Abstract:
To investigate the evolutionary patterns of initial oxidation in coal subjected to mining-induced loads due to changes in mechanical properties and pore-fracture structures, coal rock triaxial creep tests programmed-temperature experiments,FTIR and AFM techniques were employed to conduct a comparative analysis of macro and micro parameters between raw coal samples prone to spontaneous combustion and coal samples subjected to repeated loading-unloading cycles. The study revealed that during the heating-oxidation process,the oxygen consumption and CO generation rates of loading-unloading coal samples increased compared to the previous working condition. In the low-temperature stage,the critical temperature values corresponding to the “sudden drop” and “sharp rise” points of indicator gas parameters gradually decreased,while the increase in these parameters for samples subjected to three and two loading-unloading cycles diminished compared to the prior working condition. As the number of loading-unloading cycles increased,the content of aromatic hydrocarbon in oxidized coal samples gradually rose,while the content of aliphatic hydrocarbon decreased. The content of hydroxyl group first declined and then increased,and the carboxyl (-COOH) and carbonyl (-C = O) peaks exhibited a “ saddle-shaped” trend, indicating an accelerated oxidation process. The BJH specific surface area,pore volume,and adsorption-desorption differential of the coal samples progressively increased,reflecting the growth of micropores and the collapse or fission of mesopores and macropores in coal samples due to loading-unloading effects. Compared with the previous working condition,the value of micro-pore structure parameters of the first three loading -unloading cycles initially rose,then declined,and eventually approached zero. Based on comprehensive analysis of four loading-unloading cycles,it was inferred that as experimental working conditions advanced,the microporous structural parameters of coal exhibited a decreasing trend. This confirmed the existence of an optimal number of loading- unloading cycles (≥ 3) and a BJH specific surface area (≥ 27. 002 m
2/ g ) that maximize the oxidation and spontaneous combustion potential of coal. In mining faces,protective coal seams,and adjacent coal layers affected by repeated mining disturbances, the redevelopment and connectivity of cleat in coal is enhanced, and the degree of fragmentation is increased. The potential risk of oxidation spontaneous combustion is increased.