Mechanism and control technology of surrounding rock failure in return air crosscut under the superposition of mining in coal seam groups and roadway disturbance

• Reveals failure mechanism of surrounding rock under mining superposition • Proposes combined support for high-stress soft rock roadways Coal seam group mining is the core method for deep coal resource exploitation, and surrounding rock instability caused by the superposition of mining and excavation disturbances has become a critical bottleneck restricting the safe and efficient production of mines. Taking the 212 return air crosscut of a coal mine as the engineering background, this roadway is located in soft coal (rock) layers and an ultra-high stress zone, affected by the mining of multiple coal seams such as 12#, 13-2#, and 15#. The existing support system fails to adapt to high stress and large deformation, leading to severe on-site problems including roof and floor convergence exceeding 1000 mm, a maximum floor heave of 1000 mm, and U-shaped steel fracture. To address this challenge, a comprehensive research method integrating theoretical analysis, physical similarity simulation, 3DEC discrete element numerical simulation, and on-site industrial tests was adopted to systematically investigate the failure mechanism and control technology of the surrounding rock. The research results indicate that the superposition of coal seam group mining and excavation disturbances results in uneven temporal and spatial stress distribution. The radial plastic zone of the roadway expands from the shoulder and bottom corners to form a butterfly-shaped failure, while the axial plastic zone spreads along the roadway and co-evolves with the stope plastic zone. 3DEC numerical simulation reveals that the plastic zone expansion amplitude of the roadway surrounding rock is reduced by over 60% after adopting the targeted support measures, and the penetration risk of the plastic zone with the stope is completely eliminated. The elastic core area of the protective coal pillar continuously shrinks, ultimately triggering surrounding rock instability. Based on this failure mechanism, a combined support technology of "high-strength anchor bolts + grouting anchor cables + U-shaped steel sheds + shotcreting" and an advanced grouting reinforcement process for soft rock layers were proposed, establishing a collaborative control mechanism of "active surrounding rock reinforcement - passive stress bearing". Verification through on-site industrial tests shows that this technology can effectively control surrounding rock deformation: the maximum roof subsidence is limited to within 50 mm, and the floor heave is reduced to less than 30 mm from the original maximum of 1000 mm, with the overall deformation of the roadway reduced by more than 70%; the stress concentration coefficient is reduced to below 1.3, and the roadway maintenance cycle is extended from 3∼6 months to more than 2 years, successfully achieving stable control of the surrounding rock. This study reveals the core mechanism of surrounding rock failure under the superposition of coal seam group mining, and the proposed control technology provides important theoretical support and engineering practice reference for surrounding rock management in deep high-stress soft rock coal seam group mining.