Exploring the evolution of infrared radiation characteristics in coal bodies under water pressure during tunnel excavation

To address the issue of sudden water hazards encountered during coal mine roadway excavation, infrared monitoring experiments were conducted on coal seam walls at water pressures of 0 MPa, 0.2 MPa, 0.4 MPa, and 0.6 MPa. This analysis focused on the infrared radiation characteristics of the coal under varying water pressures, with the aim of providing early warning indicators for potential water burst incidents. The results indicate that during the excavation process, the stress on the coal and rock at each monitoring point in the tunnel exhibits a continuous cyclical fluctuation, with slightly higher stress observed in areas of greater water pressure. At a water pressure of 0 MPa, the infrared thermal characteristics exhibit significant alterations, with a “O”-shaped high-temperature zone appearing in the central region. At a water pressure of 0.2 MPa, a strip-shaped low-temperature radiation differentiation phenomenon is observed in the upper half, with relatively stable change characteristics. Conversely, at 0.4 MPa, an anomalously high temperature is detected in small regions of the upper half, while at 0.6 MPa, a large area of temperature decline emerges, indicating that greater water pressure corresponds to more pronounced changes in the infrared thermal imagery. At a water pressure of 0 MPa, the average infrared radiation temperature (ΔAIRT) exhibits an initial increase followed by stabilization, indicating the occurrence of local shear failure. In contrast, under water pressure conditions, the overall ΔAIRT demonstrates a downward trend, which becomes more pronounced with increasing water pressure, indicating the presence of local tensile failure. At a water pressure of 0 MPa., the temperature range R of the coal body shows a decreasing trend over time. In contrast, under water pressure conditions, the temperature range R of the coal body exhibits an overall increasing trend over time, with a faster rate of increase at higher water pressures. This indicates that greater water pressure leads to increased instability in the coal and rock, resulting in a higher degree of disintegration. The Variance of successive minus infrared image temperature (VSMIT) displays varying degrees of exceeding threshold levels at different water pressures, with higher frequencies of exceedance observed at elevated pressures, indicating a more severe degree of damage and fracturing in the coal and rock. The fractal dimension (D) of the coal and rock consistently increases over time across different water pressures, with a larger D observed at higher pressures, signifying a continuous exacerbation of damage and fracturing at each monitoring point throughout the monitoring period. In conclusion, the results of this study offer significant theoretical and practical value for employing infrared radiation technology to monitor water inrush from coal and rock in underground roadways.