Micro-seismic and acoustic emission (AE) activities resulting from rock failure are among the main parameters used for understanding the rock burst phenomenon in tunnel excavation. To evaluate the mechanism of AE behavior with rock failure, AE is measured by conducting a rock triaxial compression test. The test results are then used to evaluate the characteristics of AE behavior resulting from rock failure. The laboratory test results are subsequently compared to simulate the AE occurrence behaviors due to rock failure by using the particle flow code (PFC) method. The AE event, AE amplitude, AE frequency, and b-value that are measured by using PFC are able to simulate the actual rock failure. The simulated rock burst signals are closely related to the AE measurements obtained from the rock triaxial compression test.
Rock burst is a type of rock failure that occurs when strain energy is rapidly released by an unstable rock mass, which is usually triggered by deep underground excavation (Hoek and Brown, 1997; Rudajev et al., 2000; Beck and Brady, 2002; Weng et al., 2017). Acoustic emission (AE) is measured by conducting a rock triaxial compression test to predict and evaluate the mechanism and progress of rock burst. The AE occurrence behaviors resulting from rock failure are also simulated by using the particle flow code (PFC) method. The number of AE occurrences, waveform frequency, amplitude value, and b-value obtained from the PFC analysis are then modelled, and the analysis results are subsequently compared with the AE measurements obtained from the rock triaxial compression test. The AE occurrence behaviors obtained from the PFC simulation are discussed below along with the results of the rock triaxial compression test.
2. AE measurements obtained from the rock triaxial compression test
2.1 Testing method and equipment
As shown in Table 1, the rock specimen used for this study was hard granite. The test pieces were prepared by using a boring core with a diameter of 50 mm and height of 100 mm. Figure 1 shows the apparatus for the rock triaxial compression test and AE measurement. AE sensors were placed on the top and bottom pedestals of the stress chamber. The loading pattern was recorded by using the strain control method, and the triaxial compression test was performed at confining pressures of 0.5, 10, 20, 30, and 40 MPa. AE was measured throughout the rock triaxial compression test by using several parameters, including the number of AE events, the frequency of the AE signal wave as obtained by conducting a fast Fourier transform (FFT) analysis and by using the AE signal waveform, the amplitude value of the AE signal waveform, and b-value. All these parameters were obtained by performing calculations based on the amplitude value of the waveform (Mori et al., 2003).