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In this study, a series of impact-induced rockburst experiments were carried out by applying multilevel cyclic stresses on a cubic sandstone with a circular opening. Information on rockburst evolution was monitored using video and AE techniques together. Experimental results show that the opening in the sandstone sample was observed to undergo rock grain ejection, rock spalling and buckling in sequence. AE activity under the lower cyclic stress level followed the Kaiser's effect, while the Felicity's effect of AE was also involved at the higher cyclic stress level. Multi-axial cyclic loading can shorten the fatigue life and fatigue strength of the sandstone sample. However, the multi-axial cyclic loading can obviously reduce the AE hits and its energy rate, in which case the proportion of the AE single with low frequency is less than those under the uni-axial cyclic compression. It is also found that the failure zone in the sandstone is characterized by V-shaped notch. The depth of the failure zone is reduced sequentially under uni-axial, bi-axial, and tri-axial cyclic compression, respectively. In contrast, the extent angle of the failure zone will increase. According to the observed profiles of the failure zone, the changes of friction angle of the sandstone are interpreted by the Mohr–Coulomb strength criterion, as well as movement of the failure line due to the fatigue damage. These findings can provide insights into the study of rock failure mechanisms under various dynamic disturbances. Highlights: Impact-induced rockburst in laboratory was simulated by applying uniaxial, bi-axial, and tri-axial cyclic loadings, respectively to cubic sandstone samples with an opening. The opening in the sandstone sample was observed to undergo rock grain ejection, rock spalling and buckling in sequence. AE activity under the lower cyclic stress level can be explained by the Kaiser's effect, while the Felicity's effect of AE was also involved at the higher cyclic stress level. Failure zone around the opening in the sandstone was characterized by V-shaped notch, whose depth of the failure zone was reduced sequentially under uni-axial, bi-axial, and tri-axial cyclic compression. [ABSTRACT FROM AUTHOR]

This study aims to simulate the process of rockburst and spalling failure of roadway surrounding rock under three-dimensional stress in deep rock engineering. Utilizing an independently developed true triaxial rockburst experimental setup, the failure process of a circular tunnel under initial in-situ stress at a depth of 500 m was investigated using red sandstone with prefabricated holes. A miniature camera device and acoustic emission (AE) monitoring system were used to monitor and record the experimental process in real time. Using the collected data, the process of rockburst and spalling failure of the circular tunnel was reproduced. Finally, the difference between rockburst and spalling failure was analyzed and compared based on four aspects of stress characteristics, acoustic emission characteristics, fragment characteristics, and V-shaped notch morphology characteristics. The experimental results show that the failure of surrounding rock was more likely to occur under dynamic disturbance load, resulting in particle ejection. The spalling failure was found to be a slow and gradual static failure process. The mechanism of rockburst was more complex involving tension-shear coupling failure, whereas, the mechanism of spalling failure was simple involving a tensile failure. Compared with spalling failure, rockburst was more intense, producing more debris, and the V-shaped notch was narrow and deep. Highlights: Failure process of rockburst and spalling is reproduced in a laboratory. The stress characteristics of rockburst and spalling failure are calculated based on elastic theory. Frequency-amplitude characteristics and crack types based on acoustic emission are analyzed. The failure intensity of rockburst and spalling is investigated based on the rock fragments and morphology of V-shaped notch. The failure process of rockburst and spalling is discussed along with strain energy. [ABSTRACT FROM AUTHOR]

This paper introduces a new high-pressure servo true triaxial rockburst experimental apparatus that can realize multi-face rapid unloading in the horizontal direction. The apparatus is used to simulate different types of strain burst phenomena in deep underground engineering, such as those at roadways, roadway intersections, and pillars with three and four free faces. In the research and development process, apparatus technologies were included to overcome five key challenges: rapid unloading under high pressure, loading gap removal fixture, three-way loading alignment, symmetrical loading, and system stability after unloading. The apparatus is used to carry out multi-face unloading strain burst experiments and can fully satisfy the experimental requirements. The entire strain burst process is recorded using a high-speed camera. The apparatus can provide experimental support for strain burst mechanism research and an experimental basis for different types of strain burst research. [ABSTRACT FROM AUTHOR]