Acoustic emission precursors of static and dynamic instability for coarse-grained hard rock
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Acoustic emission precursors of static and dynamic instability for coarse-grained hard rock SU Guo-shao(苏国韶), GAN Wei(甘伟), ZHAI Shao-bin(翟少彬), ZHAO Guo-fu(赵国富) Key Laboratory of Disaster Prevention and Structural Safety of Ministry of Education, School of Civil Engineering and Architecture, Guangxi University, Nanning 530004, China © Central South University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Abstract: To investigate the acoustic emission (AE) precursors of coarse-grained hard rock instability, an experimental study on the rockburst and slabbing process of granite was carried out using a true triaxial test system. The evolution of the AE signals was monitored and analyzed in terms of the AE hit rate, fractal dimension of the AE hit number, AE count rate, b-value, dominant frequency and microcrack type. The test results show that after rock slabbing occurs, the AE precursors that can be used to predict the final dynamic instability (rockburst) are as follows: indicators such as the AE hit rate and AE count rate suddenly increase and then suddenly decrease; the AE hit rate exhibits a “quiet period”; during the “quiet period”, a small number of high-amplitude and low-frequency hits occur, and the signals corresponding to shear fracture continue to increase. The AE precursors for the final static instability (spalling) are as follows: both the AE hit rate and the b-value continuously decrease, and intermittent sudden increases appear in the high-frequency hits or the AE count rate. Key words: rockburst; slabbing; spalling; acoustic emission; true triaxial test Cite this article as: SU Guo-shao, GAN Wei, ZHAI Shao-bin, ZHAO Guo-fu. Acoustic emission precursors of static and dynamic instability for coarse-grained hard rock [J]. Journal of Central South University, 2020, 27(10): 2883−2898. DOI: https://doi.org/10.1007/s11771-020-4516-6.
1 Introduction Rockburst and spalling are the most common geological disasters in deep hard rock engineering [1]. Rockburst, a dynamic instability phenomenon (Figure 1(a)), is characterized by fragments ejecting away from the surrounding rock, while spalling is characterized by thin plate-shaped rocks spalling from the surrounding rocks, belonging to the static instability phenomenon (Figure 1(b)). Both rockburst and spalling can directly threaten the safety of construction personnel and affect project progress [2−4]. Therefore, it is urgent to improve the prediction and warning of rockburst and spalling.
Previous field experience and indoor studies have shown that slabbing is an inevitable and precursor process for strainburst in intact rocks around deep tunnels [5−7]. Historically, the phenomenon of rock slabbing has often been used to provide a warning for rockburst failure. However, it should be pointed out that slabbing failure does not indicate that the occurrence of rockburst is inevitable. This is because after rock slabbing, two distinct modes of instability may appear. One mode of instability is static spalling instability, which is characterized
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