Abstract: To obtain effective precursory characteristics of the failure of oil shale under load, we conducted uniaxial compression acoustic emission (AE) tests on oil shale using a TP coupled gas escape test system. We collected AE signals throughout the entire failure process of rock samples and analyzed the evolution of AE during deformation and failure. Employing the critical slowing down principle, we conducted an in-depth analysis of AE characteristics' variance and autocorrelation coefficient during the loading failure process of rock samples. Test results revealed significant AE phenomena throughout the testing process, with the changes in AE characteristic parameters (energy count, ring count, radiation value) correlating well with rock deformation and failure. Analysis of acoustic emission characteristics RA (rise time/peak amplitude) and AF (average frequency) indicated that the early stages of the test primarily exhibited tensile fracture, transitioning to increased shear fracture in later stages. Near peak intensity, AE characteristic parameters exhibited rapid increases, manifesting a clear critical slowing phenomenon. The sudden rise in variance and autocorrelation coefficient serves as a precursor to rock failure, with variance providing more accessible and reliable precursor information compared to the autocorrelation coefficient. By combining the b value of acoustic emission with variance of AE characteristic parameters, we effectively eliminated false signals generated during testing. The drop point of the b value in the rapid rise stage of variance slope was identified as the precursor feature point of rock failure.

Key words: oil shale, uniaxial compression, deformation failure, acoustic emission, critical slowing down, precursory characteristics