Predictions of the stratified model for negative dispersion and for dependence of the phase velocity on the mechanical properties in water-saturated sandy sediment

초록

The negative dispersion and dependence of the phase velocity on the mechanical properties for the fast longitudinal wave in water-saturated sandy sediment were investigated over a frequency range from 0.3 to 1.0 MHz. The experimental data of the phase velocity measured in our previous work exhibited a significant negative dispersion, with the velocity (mean +/- standard deviation) ranging from 1680 +/- 5 m/s at 0.3 MHz to 1590 +/- 4 m/s at 1.0 MHz. The mean rate of decline in the phase velocity was 120 +/- 20 m/s/MHz between 0.3 and 1.0 MHz. A stratified model for wave propagation in periodically stratified media consisting of alternating parallel solid-fluid layers was successfully applied to predict the negative dispersion of the phase velocity in the sediment. The dependence of the phase velocity on the mechanical properties of the sediment, such as the grain size, porosity, and density, was also predicted by using the stratified model and was compared with the predictions of the grain-shearing (G-S) model and the Wood's equation. Incorporating the relationship between the grain size and the porosity of the G-S model into the stratified model significantly improved its ability to predict the dependence of the phase velocity on the grain size.

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