Abstract: After the excavation unloading of underground engineering rock mass, the geostress in surrounding rock mass varies with the spatial position in a gradient form. The wave impedance of rock varies in a gradient form under the action of gradient geo-stress, and then affects the propagation and attenuation characteristics of stress wave. In order to investigate the effect of gradient geostress on the propagation characteristics of rock stress wave, the stress wave propagation tests were carried out on the red sandstone long specimen under nine stress gradient conditions by using the self-developed rock stress wave propagation test system with gradient static stress. By analyzing the variation laws of rock stress wave velocity and wave impedance with stress gradient, empirical models between stress wave amplitude and propagation distance, propagation time and stress gradient were established to explore the mechanism of stress wave propagation and attenuation affected by gradient stress in red sandstone. The results show that under the same stress gradient condition, the stress waveform change little with the increase of propagation distance, but the stress wave amplitude decrease gradually. With the increase of stress gradient, the stress wave velocity and wave impedance in each measuring point section of rock increase, but the increase rate gradually slows down, the wave impedance difference ratio between adjacent measuring point sections increases rapidly first and then decreases slowly. The stress wave amplitude decreases exponentially with the increase of propagation distance and propagation time, with the increase of stress gradient, the spatial-and time-attenuation coefficients of amplitude show a trend of “rapid increases at first, then slow decreases”. As the stress gradient increases, the stress wave amplitude at the same measuring point decreases rapidly first and then varies slowly, and at the low stress gradient stage, the further away from the free end, the faster the amplitude attenuation rate of the measuring point.

Key words: rock stress wave propagation, gradient stress, propagation velocity, wave impedance, amplitude attenuation