Characteristics of infrared radiation precursors of water inrush from coal and rock fractures under hydrodynamic coupling

Due to the challenging conditions associated with coal resource extraction, mine water hazards continue to pose a prominent threat. Accurate prediction and monitoring of precursor information related to water inrush events are crucial for ensuring mine safety. However, conventional monitoring techniques, such as microseismicity and acoustic emission, currently possess limitations in providing effective early warning. Therefore, this study aims to explore a novel method for monitoring mine water hazard precursors based on infrared thermal imaging technology. To achieve this, we conducted laboratory experiments to simulate the processes of rock fracture and water intrusion in coal mines. Sandstone specimens were selected for investigation under water pressures of 0 MPa, 0.2 MPa, 0.4 MPa, and 0.6 MPa. The research findings reveal that during the hydraulic coupling fracture process in sandstone specimens, the infrared thermographic parameters, including infrared thermal images, Average infrared radiation temperature (AIRT), the Variance of Original Infrared Image Temperature (VOIIT), and Variance of Successive Minus Infrared Image Temperature (VSMIT), demonstrate significant and distinct phase-dependent variations. Before a water inrush, infrared thermal images display low-temperature patches that gradually extend and expand. The AIRT shows a decline, with some instances falling by more than 0.5 °C. The VOIIT transitions from stable growth to significant fluctuations or rapid increases, reaching a maximum value of 0.776 under a water pressure of 0.4 MPa. In addition, the VSMIT exhibits abrupt changes, with the maximum value at a water pressure of 0.2 MPa increasing 10.43 times compared to the minimum value. These variations provide crucial precursor information for coal rock fracturing and water inrush events. Additionally, this study innovatively applies the Critical Slow down Theory (CSDT) to the analysis of infrared indicator parameters. The characteristics of critical transitions in the coal-rock dynamic system further enhance the precursory warning, allowing for an advanced warning time for the infrared indicators. This allows for the earliest prediction of a peak stress ratio of 51.2 %. This study successfully validates the effectiveness and timeliness of infrared thermography in capturing the infrared signals associated with rock fracturing and water inrush. Therefore, Author recommend deploying multiple infrared cameras for 24-hour unmanned monitoring in engineering projects at risk of water hazards, such as coal mine excavations and underground tunnels. Additionally, setting alarm thresholds for specific infrared indicators at the ground control station via a ring network will enable real-time monitoring and preventive measures to mitigate the risk of water inrush disasters.