Determination method for safety pillars in coal-seam gas tunnels and multi-factor sensitivity analysis

Tunneling through coal-bearing strata carries high risks of coal–gas dynamic disasters, with the determination of the safety pillar thickness constituting a critical engineering challenge for disaster prevention. This study establishes a theoretical model for tunnel safety pillars in coal measure strata under the influence of gas pressure, integrating the silo theory and the limit equilibrium methods. The research derives mechanical instability criteria for rock pillars, analyzes the multi-factor impacts on tunnel safety pillars, and investigates the plastic zone evolution processes under multi-factor conditions. Key findings indicate: (1) Under identical geological conditions, increasing the tunnel excavation radius, the coal seam dip angle, the lateral pressure coefficient, the surrounding rock classification, and the gas pressure all reduce pillar stability, requiring greater safety pillar thickness. (2) The excavation radius, the lateral pressure coefficient, and the surrounding rock classification demonstrate a significant influence on the required pillar thickness, with sensitivity ranking: surrounding rock classification > lateral pressure coefficient > coal seam dip angle > gas pressure. (3) The plastic zone evolution patterns remain consistent across different working conditions, showing intensified coal seam influence and increased outburst risks as the tunnels approach the coal seams. These findings provide crucial references for the stability analysis of reserved safety pillars in coal measure strata tunneling projects.