Three-dimensional leakage redistribution and spontaneous-combustion hazard migration under heterogeneous resistance, buoyancy, and ventilation in steeply inclined composite goafs

Spontaneous-combustion hazards in extra-thick, steeply inclined composite goafs depend on the redistribution of oxygen-bearing seepage as heterogeneous resistance dissipates mechanical momentum. This study links leakage attenuation, buoyancy-driven deflection, and ventilation-induced changes in three-dimensional hazard distribution. A three-dimensional heterogeneous porous-medium model coupled airflow, oxygen transport, coal oxidation, and heat transfer in an active goaf connected to an overlying abandoned goaf through a fractured 5 m interlayer. An SF 6 tracer test identified the principal cross-layer pathway, with a 6.67% difference between modeled and measured mean velocities. Compaction attenuated leakage from approximately 0.05 to 0.001–0.005 m s −1 , increasing the relative influence of thermal buoyancy and redirecting weak seepage toward the high return side. A saturating exponential relationship between nondimensional deflection-core height and Richardson number (R 2 = 0.9841) quantitatively characterized high-level displacement in relation to the buoyancy-to-inertia balance. Under the prescribed oxygen and velocity thresholds, increasing inclination from 0° to 36° raised the hazard volume from 3.50 × 10 4 to 4.42 × 10 4 m 3 . The maximum normal height increased from 4.5 to 12.0 m. Increasing inlet velocity from 1.5 to 2.5 m s −1 suppressed high-level deflection, reducing hazard volume by 40.0% and maximum height to 6.2 m. Meanwhile, the downstream oxidation boundary advanced from 85 to 115 m. These findings connect leakage attenuation and high-level displacement with the three-dimensional redistribution of spontaneous-combustion hazards. The empirical relationship provides a quantitative description of the deflection response, while the contrasting ventilation effects support differentiated monitoring and control of elevated cross-layer pathways and deep oxygenated regions.