Sidewall hole collapse mechanism and control technology of narrow coal pillar goaf roadway in near−horizontal thick coal seam

Severe challenges including fractured surrounding rock, intense sidewall deformation and frequent hole collapse during bolt installation commonly exist in gob−side entry driving with small coal pillars in nearly horizontal thick Jurassic coal seams in western China. Taking the return airway of Panel 2104 in Menkeqing Coal Mine as the engineering background, field investigation, mine pressure monitoring, numerical simulation and field engineering tests were combined to systematically investigate the stress evolution, deformation and failure characteristics of surrounding rock in the gob−side entry, as well as the chain evolution mechanism of sidewall hole collapse. Targetedly, an integrated surrounding rock control technology adopting drilling−bolting integrated hollow grouting bolts was developed. The results reveal that an asymmetric stress field forms adjacent to the goaf, and excavation disturbance triggers extensive unloading damage of shallow sidewall surrounding rock and the development of plastic fracture zones. The peak advance abutment pressure rises first and then declines, accompanied by continuous expansion of the stress relief zone. Disturbance induced by borehole drilling causes borehole wall collapse, generating a vicious cycle of“fracture−hole collapse−support failure−aggravated deformation”.Low coal seam strength, developed joints and weather−prone immediate roof constitute the geological prerequisites for hole collapse, while asymmetric mine pressure, high stress concentration in sidewalls and connected plastic zones act as its mechanical origins. The integrated support technology using drilling−bolting integrated hollow grouting bolts is proposed and verified via industrial field tests. Field application demonstrates that the average installation time for a single bolt is reduced from 13.16 min to 5.6 min, representing a 2.35−fold improvement in construction efficiency; cumulative sidewall deformation decreases by 78.8%. This technology effectively breaks the chain reaction between hole collapse and surrounding rock instability, and greatly improves anchorage quality and continuous excavation performance. The research findings can provide theoretical support and engineering references for hole collapse prevention and stability control of gob−side entries in similar nearly horizontal thick coal seams.