Failure characteristics and control techniques for mining roadway affected by stress accumulation of residual pillars in contiguous coal seams

During contiguous coal seams mining, the upper goaf residual pillars often cause strong ground stress in underlying longwall mining face and stress accumulation can result in severe mining roadway failure and deformation. To address this issue, the strata stress behavior of working face and the failure and deformation process of an affected roadway at Tashan coal mine were studied in this work. The failure and deformation process of the mining roadway surrounding rock were monitored using the borehole endoscope and the laser range finder. The distribution characteristics and evolution process of vertical stress and failure zone around the affected mining roadway were simulated by FLAC(3D). The mechanism of the large deformation and failure of the roadway were revealed based on the numerical simulation. The results indicate that: (1) the supports working resistance below the residual pillar are generally high with an average value of 9726.6 kN, while that below the goaf are generally low with an average value of 7655.5 kN; (2) the deformation and failure degree are relatively moderate for the affected mining roadway beyond 30 m away from the mining face, and it is relatively severe within 30 m away from P30515 working face; (3) the fundamental causes of large deformation and failure of the affected mining roadway are the combined concentrated stress of the residual pillar and the advanced abutment pressure of the working face; (4) hydraulic fracturing was adopted to degrade the residual pillar's mechanical properties based on its concentrated stress distribution characteristics, which cuts off the stress transfer path of the overburden strata and improves the stress environment of the mining roadway.