| Popis: |
Attenuation and stiffness measurements have been made on partially saturated, artificial cracks over the frequency range 2 mHz to 10 Hz. The wedge-shaped cracks are open systems composed of glass slides separated by wires. A non-zero, frequency independent attenuation has been measured at low frequencies for these cracks. Additionally, the low frequency stiffness of a partially saturated crack is larger than that of a dry crack. For this geometry and frequency range, no dissipative fluid flow is expected. Local fluid flow models predict zero attenuation and no stiffening for these open systems. We have developed a model based on the restricted motion of the fluid meniscus to explain the measured low frequency results. In this model, physicochemical interactions between the fluid and solid are responsible for restricting motion of the three phase boundary between liquid, solid and gas (the contact line). We compare model predictions with data measured in artificial cracks partially saturated with deionized water. Contact line mobility is varied by exposing the crack surfaces to increasing concentrations of sodiumdodecylsulfate (SDS) in deionized water. Increases in low frequency attenuation (below .1 Hz) and crack stiffness correlate with increasing surface exposure to SDS. These measured trends can be qualitatively modeled by reducing meniscus mobility as the surface contamination increases. |
