Experimental study on failure precursors of fine sandstone based on critical slowing down theory

In order to explore the critical slowdown characteristics and instability precursors of fine sandstone with prefabricated fractures under uniaxial loading, uniaxial loading and synchronousacoustic emission(AE) were carried out on fine sandstone samples with different prefabricated fracture angles using MTS loading system, and the acoustic emission characteristic parameters(RA/AF value, duration and rising time) in the damage and failure processes of rock were systematically analyzed based on the critical slowing down theory method. The results indicated that, under uniaxial loading, there will be a dispersion fluctuation phenomenon when the fine sandstone with prefabricated cracks changes from fracture damage to instability failure, that is, an obvious critical slowing down phenomenon, which is manifested by the sudden increase of the variance and the autocorrelation coefficient. The window length and the lag step have no significant effect on the precursory characteristics of the variance, but have a great influence on the volatility of the autocorrelation coefficient. When the window length and the lag step are small, the autocorrelation coefficient fluctuates greatly. When the window length and the lag step length are large, the autocorrelation coefficient fluctuates less. The variances of RA/AF value, duration and rising time are the sameas the mutation time of autocorrelation coefficient precursor signals, andthe waveform fluctuationsare also similar, which appears in the irreversible plastic deformation stage of new microcrack initiation. Therefore, the variances of RA/AF value, duration and rising time, and the increase of the autocorrelation coefficient of AE can be used as the precursor characteristics of instability. The autocorrelation coefficient fluctuates greatly compared with the variance. Therefore, the variance can be used as the main criterion for rock damage to instability, and the autocorrelation coefficient can be used as the auxiliary criterion. In summary, the research results can provide important reference for the short-term monitoring and early warning of rock brittle failure with sudden strong and weak external deformation such as landslide, collapse, mining and tunnel. © 2022, Science Press. All right reserved.