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| Analysis of failure characteristics in delayed strain-type rock burst simulation test on granite |
| WANG Hongjian1，2，ZHANG Jinran1，LIU Dongqiao3，ZHAO Fei1，3，SHI Xiaoshan2，4，REN Fuqiang5，WANG Chuang1 |
| (1. College of Geosciences and Engineering，North China University of Water Resources and Electric Power，Zhengzhou，Henan 450046，China；2. State Key Laboratory of Intelligent Coal Mining and Strata Control，China Coal Technology and Engineering Group，Beijing 100013，China；3.State Key Laboratory for Geomechanics and Deep Underground Engineering，China University of Mining and Technology，Beijing 100083，China；4. China Coal Research Institute，Beijing 100013，China；5. University of Science and Technology Liaoning，Anshan，Liaoning 114000，China) |
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Abstract Strain-induced rock burst can be classified into instantaneous and delayed types according to rockburst causes. In this paper，a real three-axis unloading and delayed strain-induced rock burst simulation experiment was conducted on granite using a deep-seated rock burst simulation experimental system. Based on the signal collected by the acoustic emission system，quantitative analysis of parameters and waveform was performed. At the same time，high-speed photography was used to record the process of rock burst destruction，and the characteristics of rock surface failure were observed. The occurrence mechanism of delayed strain-induced burst in granite rock was revealed from multiple perspectives. The results indicate that granite occurred severe delayed type rock burst under the special stress loading condition which referred to loading in three directions，unloading one single face and then loading in vertical direction. Before the granite occurred rock burst，the AE ringing counts had an intensive and explosive growth while the AE b-value showed a sudden continuous decline. During the rock burst phase，the proportion of AE signals with high amplitude in low-frequency showed a growth trend，indicating there occured rapid development of large-scale cracks with higher energy release in rock. Based on AE cluster analysis of RA-AF distribution division，it was found that there appeared tensile and shear composite failure，and both the amount of tensile and shear type cracks decreased at first and then had an obvious increase until final decreased. Tensile-shear crack ratio increased and then decreased，remained stable，rose and then dropped again to the lowest value. The fractal of AE ringing count rate presented dense distribution in a short period of time before burst，and had a sudden decrease sharply after the continuous vibration. Compared the warning information of rock burst determined by AE ringing count，b-value，major frequency，RA-AF distribution and AE fractal dimension，the average precursor response coefficients were 1.18%，0.94%，1.50%，1.45% and 0.91% respectively. Hence，the response time for identifying precursors based on the AE major frequency-amplitude and tensile-shear crack amount and ratio were earlier. They could more finely characterize the complexity of AE signals and reveal the rock fracture mechanism. This study can provide reference for revealing the mechanism of delayed type rock burst occurrence and establishing disaster warning methods.
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