Numerical Investigation of Gas Migration and Spatiotemporal Evolution in Y‑Type Ventilation Working Faces with Gob-Side Entry Retaining Using COMSOL.

Abstract

China has numerous gassy and outburst-prone coal mines. Y-type ventilation with gob-side entry retaining enhances resource recovery and reduces excessive gas in the upper corner but may cause gas buildup at the working face and gob-side entry retaining tail. To address this, a two-dimensional dynamic gas migration model of the goaf was developed in COMSOL to simulate gas concentration evolution under advancing speeds of 6, 9, and 12 m/d and airflow distribution ratios of 2:1, 1.5:1, 1:1, 1:1.5, and 1:2. Higher advancing speeds intensify coal disturbance and gas desorption, resulting in peak concentrations of 1.10 and 0.95% under 12 m/d. At 9 m/d, the values decrease to 0.74 and 0.48%, indicating the optimal advancing speed. Reducing to 6 m/d further lowers concentrations but shows marginal improvement, implying a threshold effect. The airflow distribution ratio significantly affects gas migration: a Z2:F1 ratio lowers working face concentration but raises gob-side entry retaining concentration, while Z1:F2 shows the opposite trend. The 1:1.5 ratio provides the most balanced result, maintaining peak concentrations at 0.62 and 0.55%. The discrepancy between simulation and field data is within 0.03, confirming model reliability. These results provide practical guidance for optimizing ventilation and controlling gas hazards in Y-type ventilated faces.