Experimental investigation on the infrared precursors of rockburst in sandstone with different bedding dip angles

In order to determine the infrared precursors of rockburst in sandstone with different bedding dip angles (beta = 0 degrees, 30 degrees, 60 degrees, and 90 degrees), four groups of true triaxial rockburst tests were carried out. An infrared thermal imager was used to obtain the infrared temperature field variation process on the free face of the sample. Additionally, the rockburst characteristics were analyzed from the stress-strain curve, failure mode of rock, Average Infrared Temperature Difference (AITD), Average Infrared Standard Deviation (AISD), and infrared thermal images, and the corresponding spectrums. Finally, based on the Nonlinear Autoregressive Model (NARX), the rockburst stress was predicted by using the AISD. The results show that with the increase in beta, the failure mode of the sandstone changes from shear failure (beta = 0 degrees) to splitting failure (beta = 30 degrees, 60 degrees, and 90 degrees). The AITD and AISD curves show a steep increase before rockburst, and the corresponding time are before rockburst 33 ms, 762 ms, 567 ms, and 316 ms, respectively for the beta are 0 degrees, 30 degrees, 60 degrees, and 90 degrees. Furthermore, the horizontal Fourier spectrums of the sandstone with inclined bedding planes (beta = 30 degrees and 60 degrees) show evident low-frequency fluctuations in a short period before the amplitude of the spectrum increases. Overall, the NARX network predicts peak stress with relatively high accuracy (greater than 85 %); however, the prediction errors of the sandstone with horizontal and vertical bedding planes (beta = 0 degrees and 90 degrees) are larger than that for the inclined bedding planes.