Experimental study on failure precursors of coal and sandstone based on two-step clustering of acoustic emission characteristics

Accurately determining the precursors of coal and rock failures is crucial for preventing associated risks in coal mines. In this study, based on the values of the four parameters amplitude, duration, counts and energy of acoustic emission (AE) signals, the AE signals of coal and sandstone samples failure were clustered by the two-step clustering method. And the precursory AE signals of sample failure under uniaxial compression were analyzed and identified. Results show that the peak of AE amplitude is before that of AE duration, counts, and energy. AE signals of both coal and sandstone samples can be classified into five types. Values of the parameters of Types I-IV AE signals of the sandstone sample are lower than that of the coal sample. The duration, counts, and energy of Type V AE signals of the sandstone sample are higher than that of the coal sample. Type V AE signals, which are middle amplitude (hundreds of mV), high duration (hundreds of thousands of mu S), high counts (about 10,000), and high energy (tens of thousands of mV*mS), account for the lowest proportion of all AE signals, at approximately 0.1%. And they began to occur at 87% sigma c of the coal sample and at 97% sigma c of the sandstone sample, respectively. Type V AE signals can be used as precursors of coal and sandstone samples failure under uniaxial compression. Acoustic emission (AE) signals were clustered based on characteristic parameters, and the features of different types of signals were analyzed based on the failure law of coal and rock. Precursory AE signals of coal and rock failures began to occur close to the peak stress with distinctive characteristics.image