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Rock disasters caused by rock fractures seriously threaten the safe and sustainable mining of deep coal resources. The infrared thermal imaging of rock fractures has a non-uniform distribution. This is important information for the monitoring and early warning of rock mass instability. In this paper, the multi-fractal theory was introduced to analyze the infrared thermal image obtained from the uniaxial loading of sandstone, which is expected to provide quantitative indicators for the infrared monitoring of rock failure. The results show that the multi-fractal parameters Δα (non-uniformity of temperature) and Δf (frequency diversity of minimum and maximum temperature) can be used to describe the distribution of the thermal field; they are sensitive to the rock macro fracture. Both Δα and Δf are constant during the initial loading stage. When the samples yield and there is a failure in the later stage of loading, the Δα and Δf change abruptly. The sudden change in Δα and Δf can be regarded as the precursor to rock failure. The research results preliminarily show the feasibility and potential of multi-fractal analysis in rock mass disaster monitoring and early warning.

Previous studies have shown that water can reduce the acoustic emission (AE) energy and other parameters during rock failure. However, the fracture mechanism of rock can be better reflected by analyzing the AE waveform. Therefore, this paper conducted experiments of uniaxial compression on sandstone samples of various water contents and collected AE signals simultaneously. Analyses of fast Fourier transform (FFT) and Hilbert-Huang transform (HHT) were performed on the AE waveform when the sample failed. The results show that as the water content increases, the frequency and intensity of the AE signal will decrease. The influence of water on the intensity of the AE signal is greater than that on the frequency. Through the analysis of the energy mechanism of rock failure, it is pointed out that the frequency and intensity of AE signal are closely related to elastic energy index W ET and burst energy index K E . The research results have guiding significance for the monitoring of rockburst.

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