关键词: 循环加卸载, 非均匀应力, 声发射特征参数, b值, 裂纹演化

Abstract: Geological conditions and mining disturbance factors induce nonuniform stress fields in rock masses, with localized zones exhibiting large stress contrasts and cyclic loading–unloading patterns during mining. To investigate the mechanical properties and acoustic emission (AE) characteristics of sandstone under nonuniform cyclic stress, cyclic loading and unloading tests were conducted on sandstone subjected to different nonuniform stresses. The relationship between mechanical parameters and AE characteristic parameters under nonuniform cyclic stress was analyzed to explore crack evolution characteristics and energy evolution patterns during cyclic loading and unloading process of sandstone under nonuniform stress. The results show that under nonuniform stress, low-stress regions in sandstone exhibit elastic rebound prior to failure, leading to stress reduction. Nonuniform cyclic stress paths deteriorate sandstone mechanical properties and failure modes, with deterioration ordered as: D-G-Z > G-D-Z > D-Z-G (D, Z, and G represent low-stress, medium-stress, and high-stress zones, respectively). The modulus of sandstone decreases significantly at failure under nonuniform cyclic stress. AE energy evolves in a stepwise manner, and AE counts show a “dense-sparse-dense” pattern. Abnormal changes in the b-value can serve as precursors to rock failure under nonuniform stress. The nonuniform stress state strongly influences crack propagation paths in sandstone: under D-Z-G, shear cracks predominate; under G-D-Z, tensile cracks predominate; under D-G-Z, composite cracks predominate. The energy curve exhibits a U-shaped trend, with high-stress regions dominating the final failure and medium-stress regions providing a supplementary role. This study provides a theoretical basis for analyzing the stability of surrounding rock in deep mining.

Key words: cyclic loading and unloading, nonuniform stress, acoustic emission characteristic parameters, b-value, crack evolution