Acoustic emission characteristics and fractal evolution of rock splitting and failure processes under different loading rates

This study aims to ensure the safe and efficient mining of No.69 tantalum–niobium ore bodies in an underground metal mine in Jiangxi Province. Brazilian splitting tests were conducted on disc samples of two types of surrounding rocks (sandy slate and granite) from the + 417 m middle section of the mine at different loading rates (0.002, 0.005, and 0.01 mm/s). The tensile strength, failure mode, acoustic emission (AE) characteristics, and fractal features of disc samples during splitting failure were analyzed in relation to the loading rate. The study demonstrates that with an increase in the loading rate, the duration of splitting failure of both sandy slate and granite significantly decreases, and the corresponding ultimate load at the time of failure significantly increases. The tensile strength of the sandy slate and granite increases linearly with the loading rate, and the growth rate of the tensile strength of the granite samples was slightly larger than that of the sandy slate. The loading rate has a significant effect on the failure pattern of the splitting process of rock disc samples. The AE ringing counts and energy of the sandy slate and granite both show an increasing trend with the loading rate. Under low loading rate, the AE ringing count signal is generally of "solitary vibration" type, and under high loading rate, the ringing count curve is generally of "group vibration" type. The peak mean values of ringing counts and energy of the sandy slate were larger than those of granite under different loading rates. The maximum values of the AE fractal dimension of both sandy slate and granite appeared between 60 and 80% of the peak stress. The research results can provide a reference for the analysis and prediction of rock stability during the design and construction of ore body mining.