When the overlying residual coal pillar is extracted from the working face at the end of mining period,the high and low thick hard roof strata of the short-distance retreat roadway is prone to joint instability,which leads to the strong deformation of the roadway and the difficulty of safe withdrawal of equipment. A mechanical model of joint instability was establised in this study for the residual coal pillar with high and low hard roof strata. The load variation of bracket was analyzed when coal mining beneath the residual coal pillar. This study also elucidated the sources of the combined instability risk in the high and low roof strata beneath the residual coal pillar during the final extraction phase. The surrounding rock optimization and control technology of high-level directional hole area hydraulic fracturing + low-level straight hole local hydraulic fracturing was proposed based on the distribution of peak abutment pressure in the roof of the residual coal pillar,the law of hydraulic fracturing fracture expansion,and the effect offracture location of low basic roof on the stress evolution of retreat roadways. The proposed control technology was successfully used in the 31107 working face of Huoluowan Colliery. The proposed technology could effectively control the high stress concentration and strong dynamic load in the final mining period,and ensure the stability of the surrounding rock of retreat roadways and the safe withdrawal of equipment.
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