Particle-scale discrete-element analysis of soundless cracking agent-induced fracture evolution in coal under laboratory-informed radial loading

Soundless cracking demolition agents (SCDAs) provide a non-explosive method for coal fracturing, but the particle-scale evolution of force transmission and bond failure under laboratory-informed loading remains unclear. This study combines free-volume expansion, steel-tube confinement tests, and a calibrated PFC2D bonded-particle model to investigate SCDA-induced fracture evolution in coal. A water-to-agent ratio of 0.28 produced the best overall response, with a maximum free-volume expansion of 333.8%. Strain-derived nominal peak pressures of 45.7–59.5 MPa were mapped to three paired diameter–pressure scenarios. Radial loading caused near-borehole contact-force concentration, outward force-chain redistribution, tensile bond breakage, particle displacement, and progressive crack propagation and coalescence. Final crack count increased from 435 to 792, while circumference-normalized crack density increased by about 30.0%. At a fixed 60-mm borehole, increasing peak pressure from 45.7 to 59.5 MPa increased final crack count from 505 to 761 and mean crack-generation rate by about 50.5%, with tensile cracks exceeding 93%. Sensitivity tests showed that particle resolution and random packing affected absolute crack statistics but not the dominant tensile radial-fracture mechanism. The results provide mechanism-based guidance for SCDA design rather than field-scale quantitative prediction.