Investigating fracture response characteristics and fractal evolution laws of pre-holed hard rock using infrared radiation: Implications for construction of underground works

As a common defect in geotechnical environments, the fracture response characteristics of holes under complex loading directly affect the catastrophic evolution mode of subsurface rock engineering. In this study, the effect mechanism of different defects on the mechanical properties and fracture damage behavior of rocks was investigated by uniaxial compression test, and the rocks fracture evolution mode with different defects was revealed by infrared radiation technology. The distribution characteristics of rock fragments and the evolution law of fractal dimension were discussed, and a constitutive model of rock damage based on the fractal dimension of lumpiness was established. Based on the results of the indoor tests, recommendations were made for the construction of the underground works, including structural design, support measures and excavation methods. It is shown that different prefabricated defects greatly influence the mechanical properties and load-bearing behavior of the specimens. Stress concentration induces crack extension and penetration and ultimately affects the damage mode of the specimen. The infrared radiation technique can sensitively reflect the anomalous response characteristics of the specimen damage process from the perspective of the temperature field. The damaged fragments have significant fractal characteristics. The constitutive model based on the fractal dimension of the block can accurately reflect the mechanical properties of the specimen. It has been verified that the fracture-damage evolution model at the laboratory scale is highly similar to the characteristics of engineering disasters. Finally, useful recommendations were made for the design of underground works, supporting structures, and excavation methods. This study will support theoretical and experimental data to further reveal the mechanism of endogenous outreach from indoor experiments to the evolutionary patterns of underground engineering hazards and management measures.