Experimental Study of Multiple Physical Properties of Tectonic Coal near a Minor Fault: Implications for Coal and Gas Outburst

Coal and gas outburst accidents often have occurred in minor faults and thick coal strips in recent years, which makes outbursts inseparable from geological structures or tectonic coal. In this paper, the coal samples near a minor fault were selected on the outburst belt, and the samples’ basic physical properties, coal fragmentation, pore structure, and gas desorption were tested. The fractal characteristics of the samples before and after crushing were innovatively compared and analyzed. The desorbed gas expansion energy and outburst potential were accurately obtained based on the particle size distribution and the gas desorption of the samples with different grain sizes. The results show that the samples have apparent fractal characteristics, and the two fractal dimensions have an obvious linear correlation, which can somewhat characterize coal fragmentation. The fault significantly increases the pore volume and specific surface area of macropores and mesopores in coal and has less influence on micropores. From 12 m outside toward the fault center, the developed macropores increase the initial gas desorption rate by 2.11–3.11 times and the first 40 s desorption volume by 1.31–2.01 times. The desorbed gas expansion energy varies from 80.70 to 383.18 kJ/m3, with the DF-0 sample being the largest and the DF-12 sample being the smallest. Overall, the coal fragmentation, gas desorption, and outburst energy show a rapid decrease first and then a slight fluctuation from the fault center to the edge. The coal body is characterized by weak fragmentation, low pore abundance, and weak gas desorption near 12 m of the fault, which traps high gas-bearing coal well and increases outburst risk near the fault center. Therefore, it is significant for precise gas extraction and outburst prevention in the fault zone.