Deformation characteristics and novel strain criteria of strainbursts induced by low-frequency cyclic disturbance

Abstract

Strainbursts induced by cyclic disturbance with low frequency (termed as cyclic-induced strainbursts) are major dynamic disasters during deep excavation and mining. There is currently no quantitative criterion available for the prediction of such disastrous events. In this study, based on true triaxial experiments, we analyzed the deformation characteristics, established two novel strain criteria for the cyclic-induced strainbursts, and explained the physical meaning of these criteria. Characteristic strains for the cyclic-induced strainbursts were defined, including the control strain ε_ctr, the strain caused by the combined dynamic and static loading ε_sd, and the ultimate strain ε_u after strainbursts. As indicated by the results, the deformation evolution of the cyclic-induced strainbursts shows remarkable fatigue characteristics, which resemble that of rock subjected to cyclic loading and unloading. In other words, there are three stages during deformation evolution, namely, initial rapid growth, uniform velocity growth after several periods of disturbance, and sudden sharp growth preceding the burst. The ultimate strain ε_u is insensitive to the tangential static stress and disturbance amplitude, but it changes nonlinearly with disturbance frequency. From the perspective of deformation, the occurrence of a cyclic-induced strainburst is controlled by the control strain ε_ctr. Thus, a control strain criterion is proposed; that is, when the stain ε_sd is larger than the control strain ε_ctr, a strainburst will be induced by cyclic disturbance. Moreover, based on the statistical results, a strain ratio criterion is proposed; that is, when the strain ratio ε_sd/ε_u is greater than 30%, a cyclic-induced strainburst will be induced.