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.