Abstract:The unloading of excavation and the complexity of in-situ stress result in the variation of static stresses in the surrounding rock. The effect of static stress on stress wave propagation was investigated with the modified Hopkinson pressure bar testing system to measure the stress wave propagation through the long specimens of red sandstone. The dynamic disturbances were approximately equal and relatively small so that the damage caused by the stress wave is insignificant. The axial static stresses were divided into 13 levels. The variation of P-wave velocity,space attenuation coefficient of amplitude,time attenuation coefficient of amplitude,and amplitude attenuation coefficient with the static stress were investigated. The results show that the stress waveforms at different locations are approximately the same when the axial static stress is constant,but there are obvious differences in the wave shapes obtained at the same location under the different axial static stresses. The tensile wave appearing at the tail of stress wave increases with the increasing axial static stress. With the increase of the axial static stress,the longitudinal wave velocity of rock increases rapidly at first,then develops gently,finally decreases sharply. The stresses of 30% and 55% of uniaxial compressive strength are two critical points. Under the same axial static stress,the amplitude of stress wave varies exponentially with the propagation distance and the propagation time respectively. As the increase of axial static stress,the spatial and time response amplitudes of stress wave decrease gradually,and both the spatial attenuation coefficient and time attenuation coefficients have the tendency of rapid decrease-steady development-sharp increase. The amplitude attenuation coefficient ?σs at the same location decreases firstly and then increases with the increasing of the axial static stress,and the ?σs at the measuring points closer to the incident side are more sensitive to the static stress than the ?σs at measuring points farther from the incident side.
SHANG J L,HU J H,ZHOU K P,et al. Porosity increment and strength degradation of low-porosity sedimentary rocks under different loading conditions[J]. International Journal of Rock Mechanics and Mining Sciences,2015,75:216-223.
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