Effect of water on the time-frequency characteristics of electromagnetic radiation during sandstone deformation and fracturing

Abstract In order to study the effect of water on the electromagnetic radiation (EMR) signals released during rock deformation and fracturing, uniaxial compression experiments were performed on sandstone samples with different water contents. During the experiments, the EMR signals were acquired. Furthermore, the time-frequency characteristics of the signals were analyzed, and their generation mechanism and the effect of water were discussed in depth. The results show that the EMR energy released decreases gradually with the increase of water content, and the EMR energy and water content can be linked by a binomial equation. For sandstone with higher water content, the precursor characteristics of EMR released in the fracturing process are more obvious. With the increase of water content, the proportion of signals in the low frequency band grows gradually, while that of signals in high frequency band falls gradually. Water reduces the macroscopic mechanical strength and fracture mechanical characteristics of sandstone, which weakens the EMR signals produced by piezoelectric effect and charge separation. Besides, with respect to the microscopic fracturing mode, the sandstone with higher water content is more likely to undergo inter-granular fracturing, which may be an important microscopic reason for the weakening of EMR of water-bearing sandstone. An EMR-based damage evolution model of water-bearing sandstone was preliminarily established, and the model helps to calculate the stress state of water-bearing rock.