The experimental investigation of rockburst is the key step to understand the failure mechanism of an underground rockmass excavation. Thus, a recently developed test facility of strain rockburst combined with acoustic emission (AE) technique was used to study the dynamic failure behaviors of some rock samples of China. Strain rockburst type was classified by the processes of rockburst experiments in laboratory, involving instantaneous rockburst, stage rockburst, and delay rockburst. The suitable study method of every stage of strain rockburst was also discussed. Furthermore, combining the strength criterion of Hoek-Brown with the strength of rock, we could not only simply determine whether the rock sample fails or not, but we could also evaluate the type of rockburst relying upon stress path. Additionally, the sources of driving force of strain rockburst were analyzed, generally including three kinds such as gravity, tectonic, and complicated gravity-tectonics. It was found that the percentage of highfrequency and high-amplitude of the AE signals for both the coal and the marble continuously increases from loading, unloading to rockburst. Finally, fractal geometry was used to describe the rockburst failure characteristics on different regards such as complex patterns of rock fragments, crack forms (intergranular crack and transgranular crack or both of them), fragments tomography distribution and fractal dimension of grain size. All these studies can motivate us to better improve the design of underground.
Rockburst frequently occurs in mining, excavation, and tunneling engineering [1, 2, 3]. Many methods have been used primarily to study the failure mechanism of rockburst in laboratory. The experimental investigations in these areas have been mainly concentrated on several aspects such as uniaxial compressive test, biaxial rockburst, triaxial rockburst test, and dynamicstatic triaxial test [4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25]. Classification, evolution process, and mechanism upon rockburst have been developed to make it possible for improving the design of underground rock engineering. For example, the rockbursts at Qinling Tunnel of China were classified into as spalling, fragment ejecting, and violent ejecting, by Gu et al [26]. Furthermore, the fractal and fracture topography analyses upon in-situ rockburst fragments were performed by SEM image method [27]. We have developed a new experimental system [33], which we call the true triaxial experimental system of strain rockburst, of treating rockmass violent failure which can be triggered by excavation, mining, and tunneling. The advantage of this special testing facility is that loading path and stress condition can be considered in rockburst test to sufficiently simulate both multiaxial stress states and opening boundaries due to underground excavation. With this test facility, abrupt unloading of the minimum principal stress in one loading face can be realized, creating stress state and boundary condition in rock sample similar to the one that exists on tunnel boundary. Furthermore, rockburst monitoring accompanied acoustic emission (AE) technique together with this system can be also used to describe timefrequency characters, occurrence mechanism, and stress path upon rockmass dynamic failure.
