Infrared radiation characteristics and fracture precursor information extraction of loaded sandstone samples with varying moisture contents

To promote the accuracy of infrared monitoring of water-bearing rock stability, sandstone samples with varying moisture contents were subjected to infrared monitoring experiments under uniaxial compression. Additionally, the temporal-spatial variations of infrared radiation were analyzed. Furthermore, the infrared precursor information of water-bearing rock fracture was quantitatively discussed in light of the critical slowing down theory. The results reveal that the infrared radiation temperature of sandstone surface decreases as the moisture content rises. Variations of maximum infrared radiation temperature (MIRT) during loading on sandstone samples present distinct characteristics in different stages. As the moisture content rises, in the early stage, the trend of MIRT decrease weakens, and the effect of stress on MIRT variation is more obvious. In the plastic deformation stage, the MIRTs fluctuate earlier and more violently. When samples finally break, the MIRTs change suddenly in a reduced range. With the rise of moisture content, the variation trend of infrared image and MIRT gradually changes from falling-rising-abruptly changing to rising-being abnormal-abruptly changing. The MIRTs of sandstone samples with varying moisture contents present the characteristics of critical slowing down during loading; and the sample with a higher moisture content exhibits more notable precursor characteristics. In addition, the variance index is more sensitive to macro-fractures than the autocorrelation coefficient and can provide more accurate precursor information for the fracture and instability monitoring of water-bearing rock.