Failure mechanism and control technology for the surrounding rock of retreat roadways beneath remnant coal pillars in close-distance coal seams

This study takes the 13,402 return airway of Sunjiagou Coal Mine as the engineering background and investigates the failure and control of surrounding rock in response to asymmetric loading and deformation instability of an underlying mining roadway affected by a remnant coal pillar in closely spaced coal seams. A combination of theoretical analysis, FLAC3D numerical simulation, borehole observation, and field industrial testing was adopted to analyze stress transfer, plastic-zone evolution, and surrounding-rock failure characteristics within the remnant coal pillar-floor-roadway surrounding-rock system. The results show that roadway stability is improved when the roadway is arranged with an outward offset or directly beneath the coal pillar. When the coal pillar width is 25-30 m and the inter burden thickness is no less than 30 m, the disturbance induced by the overlying remnant coal pillar on the underlying roadway is significantly weakened. Roof fractures are mainly developed within the range of 0-5 m. Based on these findings, an optimized support scheme involving coordinated long and short roof cables and targeted reinforcement of the roadway ribs was proposed. Field tests indicate that the deformation of the roof, floor, and both ribs is controlled within 4-5 mm. The research results can provide a theoretical basis and engineering reference for roadway layout and support design in mining roadways affected by remnant coal pillars in closely spaced coal seams.