Abstract: Rock masses in underground engineering are subjected to three-dimensional in-situ stress, which influences their physical and mechanical properties by controlling pore compaction, crack initiation, and propagation. These processes result in varying degrees of change in different ultrasonic parameters. To investigate the sensitivity of various ultrasonic parameters to three-dimensional in-situ stress and their attenuation characteristics, ultrasonic wave propagation tests were conducted on red sandstone using a three-dimensional static stress ultrasonic testing system. By analyzing the selected head waveforms, the variations of ultrasonic wave velocity, head wave amplitude and head wave energy with the three-dimensional static stress were investigated. Empirical models of rock ultrasonic parameters were developed. The sensitivity of each parameter to the three-dimensional in-situ stress was assessed, and the attenuation mechanism was explored. The results indicate that under constant confining pressure, ultrasonic wave velocity increases rapidly with increasing axial static stress and then stabilizes, following an exponential relationship. The head wave amplitude of red sandstone initially increases and then decreases, exhibiting a Gaussian distribution. Similarly, head wave energy shows an overall trend of first increasing and then decreasing. Under constant axial static stress, ultrasonic wave velocity, head wave amplitude, and head wave energy all increase with rising confining pressure, indicating that confining pressure enhances ultrasonic wave propagation. Different acoustic parameters exhibit varying sensitivities to rock damage evolution. Compared to ultrasonic velocity, head wave amplitude and head wave energy are more sensitive to both initial pore compaction and damage evolution, making them more suitable for characterizing the damage evolution of engineering rock masses.

Key words: three-dimensional in-situ stress, rock ultrasonic wave, propagation attenuation, head wave analysis, parameters sensitivity