轴向静载对红砂岩中应力波传播特性的影响试验研究

由于开挖卸荷效应以及原岩应力的复杂性,围岩体承受的静应力大小具有动态变化特点。为了研究静应力大小对岩石应力波传播的影响,利用动静组合加载试验装置,对红砂岩长试件进行小扰动的应力波传播试验,试件轴向静应力分别设置为13个等级。通过应力波传播速度和幅值随传播距离、传播时间以及静应力的衰减规律,研究不同静应力条件下应力波的传播衰减特性。结果表明,相同轴压下,不同测点处应力波形状基本相同;不同轴压下,相同测点处应力形状变化较大,轴压越大,应力波尾部出现的拉伸波越大。随着轴向静应力的增加,岩石纵波波速呈"快速增加–平缓发展–急剧减小"的趋势,轴向静应力与单轴抗压强度之比?s/?c=30%和?s/?c=55%是其2个应力分界点。相同轴压下,应力波幅值随传播距离及传播时间都具有良好的指数关系;随着轴压的增加,空间和时间响应强度逐渐减小,幅值空间衰减系数和时间衰减系数呈"快速减小–平稳发展–急剧增大"的趋势。随轴压增加,相同测点处幅值随轴压衰减系数??s先减小后增大,离冲击端越近测点处的??s变化越敏感。

Experimental study on stress wave propagation characteristics in red sandstone under axial static stress

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.