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伴随岩体卸荷过程,岩体内部应力状态要进行调整,同时岩体内部几何结构也要发生变化。由于卸荷过程应力状态变化很复杂,文中利用卸载过程中岩体内部几何结构的变化来反映卸载过程,通过岩体几何结构对弹性波传播的影响来分析卸载过程的波速。为考虑弹性波作用下局部裂纹的相互作用,采用双裂纹模型近似分析。在双裂纹体系内部采用“相互作用”分析法,以部分考虑波在岩体内的多次散射;在双裂纹体系之间采用线性叠加分析法,以考虑岩体中缺陷影响的局部化。通过节理裂隙的张开程度和节理裂隙的张开率描述卸载过程对双裂纹体系的影响,由此,对比分析了开挖卸载过程中四种不同的玄武岩与主频25 kHz和主频1 kHz对应的弹性波波速的变化。结果表明,随着卸载过程的推移,主频25 kHz声波和主频1 kHz地震波对应的相对波速逐渐减小,但声波波速的减小幅度要比地震波减小的幅度小,声波波速可以降低到原来的80%,而地震波波速可以降低到原来的50%。结论对于水利工程、隧道工程等建基面的验收和评价有很好的指导意义。
With the rock unloading process, the internal stress state of rock mass should be adjusted, meanwhile, the internal geometry of rock mass should also change. Due to the complexity of the stress state during the unloading process, the unloading process is reflected by the change of the internal geometry of the rock mass during the unloading process. The wave velocity of the unloading process is analyzed by the influence of the rock mass geometry on the elastic wave propagation. In order to consider the interaction of local cracks under elastic wave, an approximate analysis of double crack model is used. The “interaction ” method of analysis is used internally in the double-crack system to partially account for multiple scattering of waves within the rock mass; linear superposition analysis is used between double-crack systems to account for localized effects of defects in the rock mass . The effect of unloading process on the double crack system is described by the degree of open joint fissure and the open rate of joint fissure. Thus, four different basalts during excavation and unloading process are compared with those with frequency 25 kHz and frequency 1 kHz Corresponding elastic wave velocity changes. The results show that as the unloading process progresses, the relative wave velocity corresponding to the dominant 25 kHz acoustic wave and the dominant 1 kHz seismic wave gradually decreases, but the amplitude of the acoustic wave decreases less than that of the seismic wave and the wave velocity of the acoustic wave can be reduced to The original 80%, while the seismic wave speed can be reduced to 50% of the original. Conclusion It is a good guideline for the acceptance and evaluation of hydraulic engineering, tunneling and other foundations.