Dynamic mechanical response characteristics and energy evolution of sandstone under unloading subjected to low-frequency dynamic disturbance

• Coupled low-frequency disturbance coupled with confining pressure unloading replicates the intricate stress environment of deep high-stress rock masses, obtained the effects of low-frequency disturbance on the deformation characteristics and mechanical parameters of unloaded sandstone. • Integration of macroscopic and microscopic (based on acoustic emission RA-AF) elucidated the effects of low-frequency disturbances on the formation of microcracks and on macroscopic failure modes in unloaded sandstone. • The influence of low-frequency disturbances on the energy evolution of unloaded sandstone was determined by experimentation, and the dissipation ratio K ( U d / U e ) and the evolution of K under loading instability and disturbance instability were determined. In deep coal mining, unloading surrounding rock is often subjected to excavation-induced low-frequency disturbances, which may lead to progressive degradation, instability, and dynamic disasters, thereby threatening the safe and efficient recovery of deep coal resources.To clarify the effects of low-frequency dynamic disturbance on the mechanical response and energy evolution of unloading sandstone. Sandstone was selected as the test material. Three testing schemes were conducted: conventional triaxial compression tests (CTC group), confining pressure unloading tests (CTU group), and variable lower-limit triaxial disturbance-unloading tests (SCV group). The results indicate that: (1) As the disturbance load upper limit increases, the hysteresis loop evolves from a “sparse–dense” pattern to a “sparse–dense–sparse” pattern, and strain–confining pressure compliance increases markedly after disturbance. (2) Crack initiation stress shows the highest sensitivity to confining pressure unloading. Compared with CTC group, peak strength, crack damage stress, and crack initiation stress decrease by 19.01%, 23.67%, and 25.09%, respectively. The strength of unloading sandstone varies parabolically with the disturbance load upper limit, whereas the strength weakening rate (SWR) follows an exponential trend. (3) Under coupled low-frequency dynamic loading and confining pressure unloading, the proportion of shear cracks varies parabolically with the disturbance load upper limit. With increasing disturbance load upper limit, the macroscopic failure mode evolves from single shear to double shear and eventually to banded conjugate shear failure. (4) Under the combined action of low-frequency dynamic disturbance and confining pressure unloading, energy evolution is characterized by cumulative dissipated energy, accompanied by slight fluctuations or sustained reduction in elastic energy. The inflection point at which the energy consumption ratio K (= U d /U e ) shifts from a stable trend to accelerated growth can be regarded as an energy-based precursor of imminent instability; however, its identification should consider different deformation stages. The research results can provide reference for the stability control and dynamic disaster prevention of underground engineering rock mass under the coupling effect of low-frequency disturbance and confining pressure unloading.