Progressive fracture evolution and mechanical response of cavity-containing sandstone under low-frequency disturbance

During deep coal mining, interlayer rock strata subjected to high static stress and low-frequency dynamic load are prone to fracture and instability, often leading to dynamic disasters. To investigate the dynamic response of rock fracture, deformation, and mechanical behavior under low-frequency disturbances, uniaxial compression tests were conducted on perforated sandstone specimens at different loading rates. This study explores the crack evolution, fracture ejection patterns, and dynamic strain behavior of sandstone under disturbance. The results reveal the following key findings: (1) The mechanical properties of sandstone are significantly influenced by the loading rate, with peak strength increasing nonlinearly as the loading rate rises. When the loading rate increases fivefold, the average peak strengths of the single-hole, double-hole, and triple-hole specimens increase by 9.67%, 14.64%, and 9.44%, respectively. However, as the number of perforations increases, the overall load-bearing capacity of sandstone decreases, and the average peak strengths are reduced by 12.58%, 12.15%, and 13.23%, respectively. (2) The acoustic emission (AE) characteristics and stress-time evolution curves of sandstone exhibit distinct inflection points. AE activity is relatively weak during the crack initiation stage, but AE events increase sharply before failure, accompanied by an exponential rise in AE energy. This phenomenon can serve as an early warning indicator of dynamic failure in high-stress sandstone under low-frequency disturbances. (3) Based on the failure modes and the extent of surface spalling and block ejection, sandstone failure can be classified into three types. The mean σ_c/σ_z values for type Ⅰ, Ⅱ, and Ⅲ specimens are 0.959, 0.765, and 0.687, respectively, indicating significant differences in mechanical properties among different failure modes. (4) The strain distribution in the rock specimens is closely related to the number of perforations. As the number of perforations increases, pronounced stress shielding zones and horizontal tensile strain zones develop between the holes during loading, providing the main pathways for crack propagation.