Reflection measurements were conducted on water-saturated sand over the frequency range 200-300 kHz. Three reflection boundaries were used: water-sand, pressure-release-sand, and acrylic-sand. A reflection ratio technique was used to remove unknown calibration and geometric factors, permitting measurement of parameters relating to the Biot fast wave and bounding of parameters of the slow wave. The interpretation of these results was facilitated by use of a mechanical model. Measured (or bounded) parameters include acoustic impedances, effective densities, wave speeds (phase velocities), effective pressures, fluid-frame displacement ratios, pressure reflection coefficients, and material moduli. The acoustic impedance divided by the phase velocity provides the ``effective density'' [K. L. Williams, J. Acoust. Soc. Am. 110, 2956-2963 (2001)] for the fast wave. As expected, the effective density was less than the total density of the sediment (effective density =89% of total). The fluid-frame displacement ratio was 2.2 for the fast wave. These results provide strong evidence for the importance of Biot effects in water-saturated sand.
Acoustical Society of America Journal
- Pub Date:
- October 2003