Impact failure and energy dissipation characteristics of fractured coal in roadways under loading-unloading conditions

• Single-fissure, parallel double-fissure, and coplanar discontinuous double-fissure configurations were systematically investigated to elucidate the failure characteristics and energy evolution mechanisms of fissured coal across a wide range of fissure inclinations (0°, 15°, 30°, 45°, 60°, 75°, and 90°). • Roadway models incorporating different fissure inclinations and spacings were established to bridge the scale from laboratory specimens to in situ excavations, enabling a comparative analysis of the distinct damage responses of fissured roadways under loading and unloading conditions. • Field case studies were employed to validate the similarities and differences in roadway failure behavior under conditions of fully developed versus partially developed fissure systems, thereby assessing the applicability of the experimental and numerical findings to real mining environments. During underground coal seam extraction, fractured roadway coal is repeatedly subjected to loading–unloading cycles, which markedly increases the risk of instability and impact-induced hazards. To clarify the impact failure behavior and energy dissipation mechanisms of fractured coal under such conditions, laboratory experiments combined with PFC 2D numerical simulations were conducted. The impact responses of coal specimens containing a single fissure, parallel double fissure, and coplanar discontinuous double fissure were systematically analyzed. In addition, numerical roadway models with varying fracture inclinations and spacings were developed to investigate the deformation evolution of surrounding rock along loading–unloading stress paths. The results show that, under loading conditions, specimens with fracture inclinations of 0° and 90° exhibit the highest strain energy density and fail most rapidly, whereas specimens with a 30° inclination experience the least damage. The elastic strain energy accumulation capacity follows the order: coplanar non-through double fissures > single fissure > parallel double fissures. During unloading, kinetic energy and maximum ejection velocity first increase and then decrease with increasing fracture inclination; for a given inclination, kinetic energy is highest in parallel double fissures and lowest in coplanar discontinuous double fissures. For fractured roadways, impact-induced damage decreases initially and then increases with fracture inclination, reaching a minimum at 30°. Increasing fracture spacing reduces damage under loading but intensifies damage during unloading. By explicitly contrasting loading-only and loading–unloading paths, this study reveals a reversal in the role of fissure spacing on roadway damage and identifies an inclination-dependent minimum-damage regime around 30° within the tested parameter ranges. The results provide guidance for risk identification and parameterized pressure-relief design for fissured roadways under unloading-dominated mining disturbances.