Influence of water content in river sand on the self-brightening of acoustic waves

Results of laboratory experiments on the propagation of high-frequency acoustic waves (f=100 kHz) in a glass tube filled with river sand are presented. Several sand samples have been used with different water content: dry, partially and completely water saturated. It is shown that the dissipative coefficient of acoustic waves decreases with increasing wave amplitude. This ‘self-brightening’ phenomenon takes place over the whole range of moisture content, from 0 to 100%, but its degree of manifestation depends on the moisture content. The exponent of the dissipative non-linearity α, is found to be the most sensitive parameter to the moisture content and is determined on the basis of measurements. It is considered to be a good indicator of water content in porous media and provides an opportunity to measure water content in such materials indirectly by means of an acoustic method. A simple phenomenological model is presented to explain the experimental results.