Measurements of sound speed, attenuation, and normal-incidence reflection coefficient in water-saturated glass beads as a function of porosity.

Abstract

Sound propagation in water‐saturated granular sediments is known to depend on the sediment porosity, but few data in the literature address both its frequency and porosity dependency. To address this deficiency, a method to control porosity [Argo et al. J. Acoust. Soc. Am. 124, 2469 (2008)] was used to prepare artificial sediments composed of water‐saturated glass spheres (130, 265, and 530 μm diameters) with porosities ranging from 0.37 to 0.43. Through‐transmission measurements were performed for frequencies from 250 to 800 kHz to determine the sound speed and attenuation. Pulse‐echo measurements for frequencies from 0.25 to 7.5 MHz were performed to determine the normal‐incidence reflection coefficient. For both classes of measurements, the Fourier phase technique was used to analyze the data. Measurement results will be presented and compared to existing models. A Biot‐based model was found to qualitatively describe the porosity dependence of the sound speed and attenuation, but a transition to a scattering‐dominated regime was observed. [Work supported by NSF, ONR, and the Welch Foundation.]