Stress-induced failure and dynamic control of a retreat roadway under residual coal pillar degradation in longwall mining

In structurally complex longwall mining, pre excavated roadways formed by structure avoidance strategies and arranged parallel to the working face are prone to stress induced failure. This study investigates the deformation characteristics and failure mechanisms of a retreat roadway in Panel 6106 of the Hongshuliang Coal Mine, which intersects a faulted and weathered zone. Field monitoring showed that deformation intensified markedly as the working face approached the roadway, with severe roof subsidence and rib convergence observed when the face to roadway distance reduced to approximately 60 m. To clarify the stress evolution and instability mechanism, mechanical testing, theoretical analysis, and FLAC3D simulations were integrated. The results indicate a four-stage evolution of the residual coal pillar, including initial excavation stability, stress superposition, critical yielding, and complete failure, during which loss of pillar load bearing capacity promotes stress transfer to the roadway support system and triggers instability. Based on this mechanism, a three-stage dynamic support strategy was implemented and field validated, incorporating adaptive reinforcement matched to the advancing stress conditions. The staged measures effectively mitigated deformation, reducing roof and rib displacement rates by over 90 % during the critical exposure stage. The proposed monitoring and analysis workflow provides a practical basis for stability control of similar retreat roadways under complex geological conditions.