Experimental study on acoustic time domain propagation characteristics of rock under high water pressure and ground stress

Rocks bodies in underground engineering are generally subjected to water pressure and geo-stress environment, where water pressure and ground stress together control the physical and mechanical properties of the rock. The study of the influence characteristics of high water pressure and high stress on the propagation of rock acoustic waves is helpful to reveal the damage evolution and dynamic mechanical properties of the surrounding rock and the inversion of water pressure and soil stress during deep rock engineering excavations. Using a self-developed high hydraulic pressure and high stress rock acoustic test system, and multiple levels of hydraulic pressure and axial static stress were set to simulate the groundwater pressure and geo-stress environment, then the acoustic propagation tests were conducted on red sandstone and limestone. The head waveforms of rock acoustic waves were selected to investigate the relationship between wave velocity, amplitude and energy of rock acoustic waves with water pressure and axial static stress, and to construct an empirical model for the evolution of rock acoustic parameters. The results show that when the axial static stress is determined, the acoustic wave velocity of red sandstone increases and then decreases with the increase in water pressure, and the two show a good Gaussian function relationship, and the acoustic wave velocity of limestone increases rapidly and then decreases slowly with the increase in water pressure. When the water pressure is determined, the acoustic wave velocity of both types of rock shows an increasing and then decreasing trend with the increase of axial static stress. The relationship between the acoustic wave velocity of red sandstone and axial static stress follows a Gaussian function, and the change in acoustic wave velocity is significant. In contrast, the change in limestone is smaller. The axial static stress condition is determined. As water pressure increases, the first wave amplitude and energy of red sandstone initially increase gradually, but then decrease rapidly, and the head wave amplitude shows an exponential function with the water pressure. The head wave amplitude and energy of limestone first increase rapidly and then increase slowly or decrease slightly. When the water pressure is determined, the head wave amplitude and energy of red sandstone increase with the increase in axial static stress and then decrease gradually, while the head wave amplitude and energy of limestone increase rapidly with the increase in axial static stress and then decrease sharply. The research results provide a theoretical basis for the characterization of the surrounding rock state, the propagation of stress waves and the stability analysis of adjacent structures in deep rock excavations under high hydraulic pressure.