Dynamic fragmentation and fracture energy of red sandstone under sub-zero temperatures and across varying water contents

In cold regions, the fragmentation characteristics and fracture energy consumption properties of frozen rock have a significant impact on the excavation efficiency and operational safety. In this study, dynamic impact tests were conducted on red sandstone with a gradient distribution of saturation coefficients under ambient and sub-zero temperature conditions. The coupling effects of temperature and saturation coefficient on fragment size distribution, average particle size, increased surface area, energy dissipation rate, and dynamic specific fracture energy (DSFE) were investigated. Additionally, a temperature influence factor for DSFE was defined to link DSFE between ambient and frozen rock masses. Furthermore, based on fracture theory, the relationship between the average size of fragments and DSFE was established through fitting analysis. The results indicate that, under sub-zero temperatures, the average size of fragments, energy dissipation rate, and DSFE exhibit a three-stage pattern as the saturation coefficient increases: an initial decrease, followed by an increase, and a final decrease. In contrast, the increased surface area displays the inverse three-stage pattern. Both transitions occur at saturation coefficients of 0.4 and 0.8. At a fixed saturation coefficient, DSFE increases with decreasing temperature, while the increased surface area shows the opposite trend. The temperature influence factor for DSFE increases approximately linearly with decreasing temperature. Crucially, the temperature sensitivity of the influence factor intensifies at higher saturation coefficients. Moreover, DSFE shows a clear linear dependence on the cube of the average size across all temperatures and saturation coefficients. Finally, a relationship between DSFE in laboratory tests and unit explosive consumption in engineering blasting has been innovatively established through theoretical analysis using energy as a link, which can provide direct guidance for blast design in cold regions.