Investigation on tectonically deformed coal particle crushing by DEM under triaxial loading: Implication for coal and gas outburst

Abstract

Tectonically deformed coal is composed of loosely bonded and brittle particles. The effect of particle crushing on tectonically deformed coal was studied through triaxial loading tests using the discrete element method. Coal particles are highly sensitive to crushing under confining pressure. When confined pressure at 2.5 MPa, the sample behaves similarly to an uncrushed sample. The majority of boundary work is consumed by particle friction and crushing during loading. The porosity increases obviously, the granular system is transferred into fluid-like state. With an increase in confining pressure, particle crushing intensifies, resulting in a growth in weak force chains and crushing energy, and a decrease in porosity. The pattern of particle crushing is closely linked to specific force chains. Particle rotation is a significant factor affecting particle crushing, and it hinders the connection of shear zones. Crushed particles decrease porosity by filling the gaps between larger particles. After compaction, crushed particles form a crushing and compaction belt, which creates local gas sealing conditions and makes gas extraction difficult in tectonically deformed coal areas. These characteristics play a crucial role in understanding how in-situ stress impacts gas outbursts and the difficulty of gas extraction.