Experimental study of nonlinear acoustic effects in unconsolidated granular materials

Experimental results of ultrasonic wave propagation through unconsolidated granular materials are reported. Influence of the applied static pressure and the propagation distance on the linear and nonlinear acoustic properties is studied. The aim of this work is to understand better the linear and nonlinear acoustic propagation through granular assemblages when the wavelength is of the order of the bead diameter. In particular, the role of the so-called force chains is currently not well understood, as well as the influence of the contact distribution of the medium. In particular, the self-demodulation of shear wave packets with variation of the excitation amplitude is documented for different configurations of granular media (propagation distance, static pressure etc...). Modeling is currently in progress and should allow together with these results to understand better the acoustic propagation through granular assemblages.