Acoustic emission signal characteristics and its critical slowing down phenomenon during the loading process of water-bearing sandstone

In deep underground engineering, the rock mass is often in a water-bearing state. Understanding the acoustic emission (AE) signal characteristics of water-bearing rock during loading process plays a crucial role in the monitoring and prediction of dynamic disasters in deep underground engineering. Therefore, sandstone samples with varying water contents were subjected to a series of uniaxial compression experiments, and AE signals were simultaneously collected. The mechanical properties and AE signal features of water-bearing sandstone were studied, and the influence mechanism of water on AE signals was expounded. Then, with reference to the critical slowing down theory, both the autocorrelation coefficient and the variance of the AE energy sequence were calculated, and the precursor characteristics of sandstone failure with varying water contents were discussed. It was pointed out that there was a critical slowing down phenomenon in AE signal. Compared with autocorrelation coefficient, variance is more sensitive to large-scale fracture of rock and has less false signal. Therefore, the sudden increase of variance can serve as an effective precursor that indicates rock failure. Moreover, for a sandstone sample with a higher the water content, the precursor point occurs earlier and appears to be more notable.