Abstract: Variations in water pressure affect both the long-term and short-term effective stress in rock masses, thereby influencing ultrasonic wave propagation. Investigating the effects of cyclic water pressure loading on the frequency-domain characteristics of ultrasonic waves facilitates the inversion of damage evolution in deep rock masses under these conditions. Using a self-developed ultrasonic test system designed for rocks under high water pressure and ground stress, we conducted ultrasonic wave propagation tests on red sandstone subjected to cyclic loading and unloading with constant amplitude water pressure. We performed a Fourier transform on the ultrasonic head wave data and analyzed the variation characteristics of the ultrasonic wave frequency spectrum amplitudes in relation to the water pressure cycle. We defined the spectral energy transport coefficient and analyzed its variation, along with the centroid frequency and quality factor, during constant amplitude water pressure cycling. Additionally, we constructed an empirical model for the attenuation of ultrasonic frequency-domain parameters in rock. Results indicate that, under constant amplitude water pressure cycling, both the spectral area and centroid frequency show an overall downward trend as the number of cycles increases. The spectral energy transport coefficient decreases linearly as the cycle number increases. As the number of constant amplitude water pressure cycles increases, the quality factor Q decreases rapidly at lower water pressures, while it decreases more slowly at higher water pressures. These research findings are valuable for understanding the damage to rock masses in deep high water pressure environments and provide a reference for the inversion of such environments.

Key words: circulating water pressure, ultrasonic waves in rock, spectral energy transport coefficient, centroid frequency, quality factor