关键词: 循环加卸载, 声发射, 渐进损伤, 破裂模式

Abstract: In the process of underground resource exploitation，frequent mining disturbance will lead to significant unloading damage effect of surrounding rock. In order to study the progressive damage charac⁃ teristics and fracture mechanism of surrounding rock under cyclic loading and unloading，the progressive damage of sandstone under cyclic loading and unloading is studied by means of acoustic emission monitor⁃ ing and numerical simulation. The progressive damage evolution law and fracture mode of sandstone under cyclic loading are revealed，which laid a theoretical foundation for the stability evaluation of surrounding rock under cyclic loading and unloading. The results show that during the cyclic loading and unloading pro⁃ cess of sandstone specimens，the main frequency of acoustic emission signals shows obvious stratification. With the increase of the number of cycles，the low-frequency acoustic emission signals of 100~200 kHz gradually increase. Before cyclic loading failure，the average frequency centroid fractal dimension of the acoustic emission signal before the failure of the sandstone specimen is reduced to the minimum value. Un⁃ der the action of cyclic loading and unloading，the failure mode of sandstone specimens is mainly shear fracture，accompanied by dispersed tensile fracture. The stress concentration phenomenon occurs at the main shear crack，which causes the internal crack to develop along the main displacement direction，and is affected by the cross action of the derived crack and the shear crack，forming a cross failure mode domi⁃ nated by shear failure. The research results can provide a theoretical support for the support design of sur⁃ rounding rock under frequent mining disturbance.

Key words: cyclic loading and unloading, acoustic emission, progressive damage, fracture mode