This paper intends to learn more about the mechanism and failure feature of rock burst disaster in coal mines from the micro-cracks propagation characteristics in the fragments of rockburst tests in laboratory, the relationship between the micro crack propagation type of rock fragments and the damage in the process of rock burst was analyzed. The laboratory rock burst tests were carried on six basalt specimens from two locations of Baijiao Coal Mine where rock burst happened frequently. Scanning Electron Microscope (SEM) technique was used to capture the images of micro-cracks of the falling fragments in the key points during the process of rockburst under the condition of uniform magnification, the propagation characteristics of cracks were observed. The laws of crack propagation were analyzed from the quantity ratio, the area ratio, the relationship between microscopic crack type and the mineral composition, the characteristic of transgranular crack at the key points. The results showed that the crack type is gradually transitioned from the intergranular crack to the coupling crack, then to the transgranular crack. At the time of rock burst, more transgranular cracks appeared which corresponded to higher energy release; the transgranular cracks were mostly expanded in plagioclase crystal.
Rock burst is a common dynamic instability geological disaster during a process of excavation of tunnels and other underground engineering cavern under high in-situ stress conditions. Excavation unloading causes strong stress differentiation in the surrounding rock of the cavern. The elastic strain energy stored in the hard and brittle surrounding rock is suddenly released and has bursting, stripping, ejection and even throwing phenomenon (XU L S, 2005). This destructive process of rock usually undergoes evolutionary processes such as crack initiation, propagation, damage, etc. (BACKERS T et al., 2005; BENSON PM et al., 2008; CAI M et al., 2004), which the process of developing from microscopic damage to macro fracture is the process of energy dissipation.
The development of rock cracks has a great influence on the energy dissipation during the rock burst (Wang Zeyun et al., 2004). Many scholars at home and abroad had conducted indoor rock mechanics experiments and numerical simulation experiments to study the characteristics of crack propagation under different stress conditions (MONTOTO, M et al., 1981; P. Ganne et al., 2007) and characteristics of crack propagation (Yoshiji Niwa et al., 1981; S.-H. Chang and C.-I. Lee, 2004; He Qiang, 2017; ZHANG Sherong et al., 2013; Wei Gao et al., 2017), the relationship between crack characteristics and energy release (Yuan Zhenming, 2007) and the relationship between the fractal characteristics of rock burst and rock failure (Li Dejian et al., 2013; 2014) has yielded many significant results. There is an inseparable relationship between the stress conditions and energy consumption of the rockburst and the microcrack propagation characteristics of the fragments generated by the rockburst. Therefore, the study of crack propagation law of rockburst fragments can provide a basis for the energy release mechanism of rockburst. (Li Dejian et al., 2010).
