Experimental study on uniaxial compression acoustic emission characteristics of fractured coal under dynamic disturbance

In actual coal mining operations, fractured coal are frequently subjected to various dynamic disturbances, fractured coal undergoing cumulative impacts follows a "damage accumulation-fracture propagation and coalescence -performance degradation" evolutionary path. To Study the mechanical properties of fractured coal samples under dynamic disturbance effects is helpful to reveal their failure and instability mechanisms. In this study, a simple impact hammer device was used to apply dynamic disturbance to the fractured coal samples, and then uniaxial compression and acoustic emission (AE) monitoring were conducted on the fractured coal samples under subjected to different numbers of dynamic disturbances. The evolution of strength and deformation characteristics, AE counts characteristics, three-dimensional AE event localization, and crack classification based on RA - AF values were systematically analyzed. The results show that the uniaxial compressive strength, elastic modulus, and peak strain of fractured coal decrease progressively with the increasing number of disturbance impacts. The reduction of uniaxial compressive strength follows an exponential function, and samples with a prefabricated fracture inclination of 30° exhibit the weakest deformation resistance. The accumulated AE counts shows a two-stage evolution pattern characterized by a gradual increase stage followed by a sharp increase stage. Moreover, the total number of AE counts decreases with increasing disturbance impact times, indicating reduced energy accumulation and earlier damage initiation. Dynamic disturbance cause a transition in the failure mode of fractured coal from brittle failure, dominated by high-energy, concentrated crack bursts, to dissipative failure, characterized by slow energy release and gradual crack propagation. The failure mode of fractured coal evolves from tensile-shear mixed failure to shear-dominated failure under cumulative dynamic loading. The research results can provide a scientific basis for the disaster prevention and control as well as stability evaluation of fractured coal under complex disturbance environments. • Dynamic disturbance has a significant impact on the microstructure and macroscopic mechanical properties of fractured coal. • Coal with a prefabricated fracture inclination of 30° are most prone to failure. • Dynamic disturbance alters the failure mode of fractured coal.