High-frequency dispersion from viscous drag at the grain-grain contact in water-saturated sand.

Shear viscous drag within the thin fluid film at the contact between grains in water-saturated sand is an important loss mechanism for high-frequency sound in the Biot-Stoll plus contact squirt flow and shear viscous drag (BICSQS) model [J. Acoust. Soc. Am. 116, 2011-2022 (2004)]. Couette flow was assumed for the shear drag but it breaks down when inertial effects within the film become significant. Using Biot's method, a correction is derived for the shear drag and inserted into the BICSQS model. The result is a prediction of negative sound speed dispersion, consistent with dynamic theories of fluid-filled poroelastic bodies.