Acoustic response characteristics of damage and instability precursors of rocks with different lithologies

Uniaxial compression and acoustic emission (AE) tests were conducted on sandstone, marble, and granite specimens to investigate the damage and instability precursors of rocks with different lithologies. The AE event rate, autocorrelation coefficient and variance of AE event rate, proportion of main frequency signals of each level of AE, r value, and proportion of two types of AE signals were analysed to determine the damage and instability precursors of rocks with different lithologies during the loading process. Studies have revealed that the size of a rock’s AE low event rate missing portion is consistent with the order of the elastic modulus and peak stress of granite, marble, and sandstone, corresponding to the severity of the rock fracturing. The autocorrelation coefficient and variance of the event rate suggest that the damage precursors of three types of rock occur earlier and last longer as the rock strength increases. The low-frequency AE signals of the three types of rocks converge to large values when the rock approaches instability and failure. It should be noted that granite experiences a downward shift in the mid-frequency band before it experiences instability. The proportion of low-frequency AE signals initially decreases and then increases when the specimen is about to become unstable. In addition, at medium and high frequencies, it initially increases and then decreases. This phenomenon becomes more pronounced as the rock strength increases. Immediately before rock instability occurs, the r value is high, and a large number of shear-like AE events occur inside the rock, exacerbating the internal failure of the rock. The proportion of single peak AE signals and bimodal AE signals fluctuates, but their evolutionary trend is opposite. The AE signal with a single peak is a precursor to the occurrence of critical instability. It initially increases and then quickly decreases.