Mechanics and Acoustic Emission Fractal Characteristics of Surrounding Rock of Tantalum–Niobium Mine Under Splitting Condition

To ensure the safe and efficient mining of the tantalum–niobium mine body No. 69 in an underground metal mine in Jiangxi province, Brazilian splitting tests were performed on sandy slate, metamorphosed sandstone and granite surrounding rocks in the middle + 417 m section of the mine, and the deformation process, failure mode and evolution law of acoustic emission of splitting failure were studied. The relationships among acoustic emission ringing count, energy, cumulative ringing count, accumulated energy, and stress and time in the process of splitting and failure of the three types of surrounding rocks were obtained. The acoustic emission ringing count and energy were generally at low levels and increased with stress. When failure occurred, the ringing count and energy both reached a peak, which can be regarded as the precursor signal characteristics of rock tensile failure. On this basis, the fractal characteristics of acoustic emission were studied. The fractal dimension of the three rock samples varied roughly in the same way, exhibiting four stages: rise → fall → rise → fall. Among them, in the period of approximately 310–425 s, the sharp decrease in the fractal dimension of acoustic emission of metamorphosed sandstone was the longest, and the acoustic emission ringing count and energy surge were the most significant. Before failure, most of the three surrounding rocks experienced a continuous decline from the largest to the smallest fractal dimension, and the change rule of the ringing count and the fractal dimension value of energy from the largest to the smallest continuous decline was obtained, which can be used as the precursor characteristics of rock instability failure. The results of this study have reference value for the analysis and prediction of rock mass stability during mining design and construction of tantalum–niobium mines.