Evolution characteristics of temperature fields of rockburst samples under different stress gradients

To study the influence of gradient stress on the evolution characteristics of the temperature field during rockburst, the gradient and hydraulic-pneumatic composite loading true-triaxial apparatus was used to perform the rockburst tests under true-triaxial gradient loading. The temperature data of the unloading face of each sample under gradient loading were continuously recorded using the infrared thermal imager until the rockburst occurred. For the high-temperature points in temperature field, the variance-mean ratio (VMR) was introduced and the relative average temperature of high-temperature points (RAHPT) was proposed for joint analysis to quantify the evolution characteristics of temperature field. It was found that (1) the VMR and RAHPT adopted in this paper successfully reflect the evolution characteristics of the temperature fields of all the samples under different stress gradients. The VMR and RAHPT increase initially with the increasing loads but subsequently show upward or downward trends in the late stage of loading under different stress gradients; (2) the VMR and RAHPT curves of each sample exhibit similar trends and obvious changes in phase with the increasing load; (3) the samples show obvious differences in rockburst precursors under different stress gradients, and the temperature differentiation of unloading faces appears shortly before the rockbursts, accompanied by the sudden increases in the VMR and RAHPT curves under high stress gradients; (4) the temperature anomalies that occurred on the samples under loading indicate the damage zones of the impending rockbursts. The research results provide a theoretical basis for infrared early-warning technology of rockbursts in underground openings.