Effect of dynamic loading on the propagation velocity of stress waves in red sandstone under axial static stress

Due to the excavation unloading effect and the amplitude attenuation of stress wave, the rock masses locating the different distances away from the blasting source are subjected to different geostress and impact loadings during the blasting excavation of underground rock mass. To study the influence of different impact loading and geostress on the propagation velocity of rock stress wave, a modified Split Hopkinson Pressure Bar (SHPB) system is used to carry out the stress wave propagation test on red sandstone, axial static stress and impact velocity of 7 sizes were set respectively to simulate the size of in-situ stress and impact load in engineering. Based on the time difference between the starting points of the incident and the transmitted waves, the propagation velocity of the stress wave at the starting point of the rock is calculated. The effects of static stress and impact velocity on the propagation velocity of stress wave are analyzed. The empirical model of stress wave propagation velocity and impact velocity is established. The variation of fitting parameters with axial static stress was explored. By measuring the acoustic wave velocity of rock after impact test, the variation law of acoustic wave velocity of rock under load with impact velocity is obtained, and the influence mechanism of impact load on the propagation velocity of rock stress wave is explored. The results show that the stress wave propagation velocity of rock with axial static stress increases first and then decreases with the increase of impact velocity, and the two are gaussian function. Axial static stress significantly affects the relationship between stress wave propagation velocity and impact velocity, and each fitting parameter shows different variation trend with the increase of axial static stress. Under different axial static stress conditions, the acoustic wave velocity of rock under load presents a trend of "gently decreasing to sharply decreasing" with the increase of impact velocity. The results are helpful to the analysis of stress wave propagation in blasting excavation of deep engineering rock mass and the stability analysis of adjacent structures.