Propagation of sound in sands: measurements and modeling

The authors have adapted devices, developed by Institut d'Acoustique et de Me/spl acute/canique for characterization of aerial sound absorbing materials, to the cases of natural sandy sediments. The authors show that all the parameters can be measured with these devices, with different approaches and precision, depending on the wanted parameters. The obtained values are consistent with previously published data and the authors notice that these parameters can vary in a large range depending on the sand considered, especially on its granulometry. The second part of this work deals with measurement of sound speed in water-saturated sand. The authors obtained dispersion curves for various sizes of sand. They all display a decrease of wave speed with increasing frequency whereas Biot theory predicts the opposite. Moreover, the authors never observed the "slow wave" the second compressional wave predicted by Biot. These two points lead to the conclusion that Biot theory is not directly applicable to water-saturated sand. The main explanation can be provided by the fact that sand is a granular medium and it is difficult to characterize a rigid skeleton in that case. A promising aspect of this work is the relation of sound speed to grain-size and permeability of the sand.