Ultrasonic properties and damage expression of frozen soil-rock mixture with various block conditions

The variation of ultrasonic parameters is closely linked to the mechanical properties and damage evolution of rock and soil mass. In this paper, uniaxial compression tests and real-time ultrasonic monitoring technology were used to explore the strength, deformation and damage characteristics of frozen soil-rock mixture (FSRM) with different block sizes and gradations, as well as the law of ultrasonic wave propagation. The results indicate that: (1) A wider gradation of rock blocks corresponds to a higher specimen strength and a lower breakage degree of rock blocks. Within the same gradation, specimens with smaller block sizes have higher strength. Wider gradation and smaller particle size of rock blocks exerts a delayed effect on damage and failure of FSRM. (2) The particle size of rock blocks plays a key role in the variation of ultrasonic parameters. Within the same gradation, the specimens with larger block sizes possess higher wave velocity and lower first wave amplitude. The effect of gradation on ultrasonic parameters is attributed to the variation of block size. (3) With the first wave amplitude as damage state variable, a damage prediction model based on the improved Duncan–Chang model is established, demonstrating superior prediction potential on the stress–strain curves of FSRM. The research confirms and promotes the quantitative correlation between ultrasonic parameters and mechanical properties of geotechnical materials, which may provide theoretical support for testing and evaluating the mechanical properties of roadbed filling in cold mountainous areas.