Experimental investigation of dry and water injection sandstone under biaxial compression loading based on the infrared and DIC technology

To investigate the mechanisms of rock crack initiation, propagation and coalescence under stress-hydraulic coupling conditions, the infrared thermography and Digital Image Correlation (DIC) technology were employed to simultaneously monitor the fracture process of dry and water injection sandstone samples under a biaxial compression loading. Subsequently, the thermal effects and deformation evolution during crack development and propagation were analysed. Furthermore, to enhance the visibility of surface cracks on the rock samples, various algorithms were applied to improve the quality of infrared thermograms. The experimental results indicate that the Non-Uniform Correction (NUC) algorithm significantly improves the clarity of infrared thermograms, facilitating more accurate crack identification. Then, by introducing the temperature gradient index (Tgi), the abnormal thermal effects on the surface of rock samples during crack growth were illustrated. It was found that the Tgi exhibits sharp fluctuations prior to rock sample failure, attributed to thermoelastic and frictional heat effects and thermal effects of crack propagation. Moreover, the thermodynamic characteristics of crack propagation were elucidated through the integration of stress gradients and temperature gradients. The findings provide valuable insights into the dynamic behaviour of rock fracture and seepage under coupled stress-hydraulic conditions, contributing to the prediction and prevention of water-related accidents.