Acoustic and thermal anomaly signals and sensitivity coupling analysis of water-saturated and dry sandstone damage

In order to further study the precursor temporal signals of damage in water-saturated and dry sandstones, as well as the dynamic sensitivity changes of acoustic and thermal signals, uniaxial compression tests were conducted on sandstones with different water content states, with real-time monitoring of internal acoustic emission (AE) signals and surface thermal infrared (TIR) signals. Research has shown that during the damage process of water-saturated and dry sandstones, TIR anomalies appear first, followed by AE anomalies. The time lag between the first appearances of TIR and AE anomalies in water-saturated sandstone is shorter than that in dry sandstone, indicating the detrimental effect of water. This time lag is of great significance for determining the degree of internal and external damage and the precursor of instability failure in rock samples. The order of sensitivity indicators for acoustic and thermal signals in water-saturated sandstone is as follows: combined acoustic-thermal signal > TIR signal > AE signal; for dry sandstone, it is: combined acoustic-thermal signal > AE signal > TIR signal. The sensitivity of the combined acoustic-thermal signal is significantly higher than that of individual acoustic or thermal signals. Therefore, in practical engineering, it is necessary to analyze the coupling of acoustic and thermal signals when analyzing the precursors of instability.