Abstract: Rock size is an important factor influencing its mechanical behavior. Rock burst is a special mechanical response of rock under complex stress conditions. The study of size effect on rock behavior in rock burst is of great importance. A modified true-triaxial apparatus and acoustic emission (AE) monitoring system made by Physical Acoustics Corporation are used to perform laboratory rockburst simulation tests on granite specimens with different heights. The fracture characteristics of rock are observed, and the AE waveforms spectra characteristics are studied. The experimental results indicate that the critical failure stress of rock samples has an increasing trend as the sample height decreases. The fracture surface characteristics of rock after rockburst have undergone a transition from splitting tension failure to shear failure with the decrease of specimen height. Meanwhile, AE energy rate, which can reflect rock damage, increases gradually as the sample height decreases, indicating faster release rate of AE energy. Using fast Fourier transform (FFT) to process extracted waveform files at typical stages, it can be found that rock samples with different heights have a similar variation in the major frequency, which transits from low frequency to high frequency and finally back to low frequency. The most important characteristic frequency, is located in the lower frequency ranges of 90~120 kHz. The high frequency part of the spectrum characteristics varies with the height of the specimen.

Key words: rockburst test, granite specimen, different heights, acoustic emission, spectra characteristics