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Failure study of weathered granite based on critical slowing down theory and acoustic emission b-value

Huang Qizheng, Zhao Kang, Yan Yajing, Wu Jun, Nie Qiang, Chen Jiale, Xiao Weiling, Wang Huiping

Archives of Civil and Mechanical Engineering

2023

Vol. 23, no. 3

art. no. e196, 2023

To investigate the precursor characteristics of failure of weathered granite (WG), we conducted uniaxial compression tests on WG specimens using the RMT-150C rock mechanics testing system and the PCI-II acoustic emission (AE) device. We analyzed the AE parameters based on the critical slowing down (CSD) and AE b-value theoretical methods. The study shows that the peak strain value of WG under uniaxial compression is < 1% and the stress falls off rapidly after the peak, and the specimen mainly undergoes brittle failure. The failure process can be divided into four stages: compression stage, elastic deformation stage, plastic development stage, and post-peak failure stage, in which the compression stage lasts longer. The ringing count rate and its cumulative amount can effectively indicate the process of WG failure during loading. As the failure nears, microcracks within the WG accumulate and expand, leading to the appearance of macroscopic cracks. At the same time, the cumulative ringing count rate increases rapidly while the ringing count rate converges to the peak. Furthermore, the rapid increase of autocorrelation coefficient and variance obtained from the CSD theory analysis of ringing counts can be used as a precursor signal of WG failure. The “inflection point” before the sharp rise of the variance curve can be regarded as an early warning point of failure. Based on the characteristic that the b-value shows a large rate fluctuation decrease before the failure of WG, the autocorrelation coefficient and variance variation law obtained by CSD theory and the early warning point are analyzed simultaneously with the b-value variation law, which can accurately grasp the failure characteristics of WG in mines.