In this study, we evaluate the changes in ultrasonic signatures (i.e., frequency content, velocity, amplitude, and attenuation) due to stress-induced alteration of fracture aperture/permeability. Flow-through experiments were performed on artificially-fractured phyllite specimens along with the concurrent measurements of ultrasonic signatures under different stress conditions. Increasing pore pressure led to fracture opening, as indicated by increases in both mechanical and hydraulic apertures. In addition, we observed that increase in confining pressure (and decrease in pore pressure) led to increases in ultrasonic velocities, ultrasonic amplitudes, and fracture specific stiffness, and decrease in ultrasonic attenuations. It was found that time-frequency partitioning depends on hydraulic aperture. The higher frequency band, for both P- and S-waves, was insensitive to the changes in stress conditions; the lower band was sensitive to the changes in stress conditions, as long as the hydraulic aperture was changing. Three-Element rheological and Power-Law models successfully predicted the time-dependent fracture displacement, with the former being more accurate at higher levels of pore pressures.

在这项研究中，我们评估了由于应力引起的裂缝孔径/渗透率变化而引起的超声特征（即频率含量，速度，振幅和衰减）的变化。在人工破裂的千枚岩标本上进行了流通实验，并在不同的应力条件下同时测量了超声波特征。孔隙压力增加导致裂缝张开，如机械和液压孔的增大所示。此外，我们观察到围压的增加（孔隙压力的减少）导致超声速度，超声振幅和裂缝比刚度的增加，以及超声衰减的减少。发现时频划分取决于液压孔径。对于P波和S波，较高的频段对应力条件的变化不敏感；只要液压孔不断变化，下带对应力条件的变化就会敏感。三元流变和Power-Law模型成功地预测了随时间变化的裂缝位移，而前者在较高的孔隙压力水平下更准确。