An insight from energy index characterization to determine the proneness of rockburst for hard rock

Abstract

The evaluation index and classification criterion of coal bursting liability are often used to evaluate hard rock rockburst proneness. In view of the great difference between the engineering conditions of embedding rocks (hard) and coal seam (softer), the evaluation results of rockburst proneness of hard rock are not accord with the actual situation. Aiming at this problem, rockburst tendency indices were studied by laboratory test in this paper. Based on the analysis of the data, it is concluded that the peak-strength strain energy storage index WETP and residual elastic energy index AEF can reflect the energy and rockburst proneness of hard rock from the elastic energy storage and residual elastic energy. By designing the cyclic loading and unloading test and the uniaxial compression test of rock, the loading rates of the above two kinds of energy indices were determined, and the determination and calculation process of the above two kinds of energy indices were clarified. The experimental results show that the linear elastic energy storage law obtained by cyclic loading and unloading of one sample is not very different from that obtained by multiple samples, both methods can be used for measurement. The peak-strength elastic energy density, pre-peak total input energy density and post-peak failure energy density of rock increase slightly with the strain rate, and the degree of rock fragmentation also has the same trend. The energy index of rock cannot fully reflect the rockburst proneness of rock. Based on the test process and results, in the case of hard rocks, 0.3–1 mm/min could be used for displacement control mode, and 50–140 kN/min should be used for load control mode. Extensometer or instrument sensor can be the strain acquisition methods.