Dynamic measurement of sediment grain compressibility at atmospheric pressure: acoustic applications

Under certain conditions, Wood\´s equation can be used to predict sound speed in fluid/solid-grain suspensions if the bulk moduli and densities of the grains and fluid are known. In this paper, that relationship is used to estimate grain-bulk moduli in suspensions where sound speed, fluid density, fluid bulk modulus, grain density, and particle concentrations are known or accurately measured. Measured values of grain-bulk moduli for polystyrene beads suspended in water (mean = 4.15 × 10⁹ Pa) and soda-lime glass beads suspended in a "heavy liquid" (mean = 3.8 × 10¹⁰ Pa) are consistent with the values of bulk moduli for polystyrene beads and soda-lime glass beads found in the literature (3.6 to 4.2 × 10⁹ Pa and 3.4 to 4.0 × 10¹⁰ Pa, respectively). These measurements thus provide controls, which demonstrate the validity of the suspension technique to estimate values of particle bulk modulus. The values of bulk modulus, measured using the same suspension techniques, for Ottawa sand and quartz sand grains collected from the coastal sediments of the northeast Gulf of Mexico ranged between 3.8 and 4.7 × 10¹⁰ Pa, with 95% confidence limits between 3.0-5.7 × 10¹⁰ Pa. These measured values of bulk modulus are consistent with the range of handbook values for polycrystalline quartz (3.6 to 4.0 × 10¹⁰ Pa). The use of the lower bulk modulus (i.e., 7.0 × 10⁹ Pa) recently suggested by Chotiros is therefore inappropriate and traditional handbook values of sediment grain-bulk moduli should be used as inputs for sediment acoustic modeling.