三轴循环加卸载裂隙砂岩渗透性演化规律研究OA

The permeability change of coal and rock induced by repeated mining during coal seam group exploitation is a key factor restricting mine gas drainage.To explore the permeability evolution law un-der repeated mining,the permeability tests on fractured sandstone with different prefabricated dip an-gles were conducted under cyclic loading and unloading.The permeability evolution mechanism was re-vealed.The results indicated that:① Fractured sandstone permeability generally declines,then slowly increases and suddenly surges during cyclic loading and unloading.In each cycle,permeability chan-ges from"decrease-increase-decrease"to"increase-increase-decrease".The end of the unloading phase can be used as a pre-extraction point for gas drainage.② With more cyclic loading and unloa-ding,instability and failure of fractured sandstone with different dip angles intensify,and permeability increases more significantly.③ Fractured sandstone with a dip angle of 45° and 60° has higher devia-toric stress sensitivity coefficients and irreversible permeability damage rates,and the former decreases with increasing confining pressure.④ Fracture dip angles affect the stress field around fractures,influ-encing fracture initiation and propagation,thus altering permeability.At the final failure stage,the per-meability of fractured sandstone with different dip angles increases by 2-9 times.The research findings have significant implications for gas drainage in coal seams and safe mining operations.