Biot model of sound propagation in water‐saturated sand

Elastic theory of wave propagation and the measured speed of sound in sandy ocean sediments indicate that such sediments are impenetrable to high‐frequency sound at shallow grazing angles. The speed of sound in water‐saturated, unconsolidated sand is in the region of 1700 m/s which, under the elastic theory of wave propagation, gives it a critical grazing angle in the region of 28°. At shallower grazing angles, refraction is not permitted, and total internal reflection is predicted. Recent experimental measurements contradict this view. Biot’s theory of acoustic propagation in porous sediments is the most likely explanation. Biot’s theory of acoustic propagation, as it applies to water‐saturated sand, is reviewed. The speed of the slow wave is found to be higher than previously predicted. New input parameter values are deduced.