Fracture evolution and nonlinear characterization of thermally damaged sandstone under uniaxial compression based on acoustic emission parameters

To explore the fracture evolution of thermally damaged sandstone during loading, this paper carried out uniaxial compression tests on sandstone specimens after different temperature treatments and collected acoustic emission signals during loading. Based on the experimental results, the dynamic evolution of the rock fracture mode was analyzed, and the nonlinear characterization parameters were calculated. Finally, the influence of temperature on the rock fracture evolution was discussed. The results show that (1) the rock strength gradually increases with increasing treatment temperature from 25 to 400 ℃, and the failure process shows a “sudden” evolution characteristic; when the temperature exceeds 400 ℃, the rock strength gradually deteriorates, and the bearing process shows a “progressive” damage accumulation process. (2) When the temperature is lower than 400 ℃, tensile failure-induced cracks are significantly dominant during the rock failure process, while at treatment temperatures higher than 600 ℃, the proportion of shear cracks increases significantly, and the dominance of shear failure mode gradually appears with increasing temperature. (3) The nonlinear dynamic evolution process of the thermally damaged rock during loading includes the transformation between disorder and order. However, when approaching destruction, the sandstone undergoes a self-organizing evolutionary process from chaos to order, which is independent of temperature, indicating that the appearance of the macrofracture zone is the final indicator of the orderly development of the cracks. The research results can provide guidance for understanding the process of thermal damage to surrounding rock masses and analyzing their stability characteristics in engineering practice.