Abstract
To explore the failure precursors of hard rock, a series of triaxial loading and unloading experiments were carried out on sandstone sample using the acoustic emission systems. The extreme-point symmetric mode decomposition method (ESMD method) was used to denoise and reconstruct the AE data. The AE quiet period in Scheme I becomes much more obvious with the confining pressure increasing, which can be regarded as the precursor information of the sample failure under conventional triaxial compression. Unlike Scheme I, there are no obvious precursory characteristics before failure in Schemes II and III, and the count rate reaches the maximum at the peak point. When the stress ratio ranges from 0.8 to 1.0, the fractal values of acoustic emission can be used to investigate the failure precursors of samples at a lower confining pressure. When the time ratio is greater than 0.8 under higher confining pressures, the fractal values of sandstone samples under unloading paths are rapidly reduced, which can be used to predict rock failure at higher confining pressures.
Highlights
The rock material properties, various stress paths, and wall rock conditions are complex and diverse, severely restricting the study on failure precursors of rock materials
Chmel and Shcherbakov [12] carried out experimental study on the acoustic emission (AE) characteristics of compression and dynamic fracture in granite, which contributes to assessing the relationship between events occurring under nonequilibrium conditions
Three triaxial compression tests on granite samples were carried out by Thompson et al [14], and new observations of fracture nucleation were proposed according to AE monitoring
Summary
The rock material properties, various stress paths, and wall rock conditions are complex and diverse, severely restricting the study on failure precursors of rock materials. The deformation and failure behavior of rock are the process of the inner micro cracks initiation, propagation, and coalescence [1,2,3,4,5] During this process, the strain energy is continuously released in the form of the elastic wave, which is referred to as the acoustic emission (AE). Based on the biaxial compression tests, Baddari et al [13] adopted electromagnetic radiation and acoustic emission to study the failure process of large rock samples, and the results can provide an analysis platform for forecasting the dynamic disaster. Zhang et al [16] performed the uniaxial loading to research the AE characteristics of rock failure process, and the AE parameters such as cumulative AE events, AE energy release rate, and the b-value were used to investigate the precursory information of rock failure. Based on the fractal theory, the influence of unloading paths on AE characteristics was quantified, which could be used to explore the failure precursors of rock and provide a theoretical basis for assessing and preventing the stress-induced stability of hard rock
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