Mechanical response and failure characteristics of coal-rock combination under different loading rates

To investigate the mechanical behavior and failure characteristics of underground coal-rock combiation under different loading rates, sandstone-coal combination with a height ratio of 1∶1 were prepared and subjected to uniaxial loading tests at four different loading rates. The acoustic emission signals during the loading process was real time monitored. The average particle size of debris and the proportion of far field debris mass were calculated to quantitatively evaluate the degree of damage. The strain rate effect of the mechanical properties and failure characteristics of coal-rock combinations were analyzed. The results show that the uniaxial compressive strength, elastic modulus, degree of coal sample fragmentation, and brittleness characteristics of the combiation are positively correlated with the loading rate. Under high loading rate conditions, the influence of heterogeneity on the mechanical behavior of the combiation is weakened. The peak value of acoustic emission ringing count increases with the loading rate, indicating an increase in single acoustic emission intensity and an increase in the severity of internal single micro fractures. Under higher loading rates, the combination has high strength, and the degree of coal sample fragmentation and briteleness characteristics and enhanced.