Laboratory measurements of acoustic properties for marine fluid-mud deposits

摘要

Knowledge about fluid mud acoustic properties is a key to understanding acoustic wave propagation in sediments and is very important for military oceanography and ocean engineering, especially for the typical rapid depositional areas of estuaries and coasts. The acoustic parameters of fluid mud are essential to the in-situ measurement of the thickness and physical properties of fluid mud. In this paper, we examine the acoustic properties of fluid-mud deposits that were experimentally formed in a settling tank during the natural settling processes of natural seabed sediment. The relationships between the acoustic properties and the sediment's physical parameters were then analyzed based on Principal Component Analysis (PCA). Results demonstrate that the sound velocity of fluid mud changes with mean grain size, clay content, silt content, and sediment concentration, with no obvious frequency dependency. For the fluid mud with the mean grain size ranging from 4.54~6.434 μm, clay content ranging from 8.25~28.85%, silt content ranging from 66.33~72.88%, sediment concentration ranging from 0.32~1.29 g/cm3, sound velocity changes from 1371.4 m/s to 1648.4%. In terms of a single variable, sound velocity showed an increment with sediment concentration and a decrement with mean grain size and clay content both with a nonlinear dependence, but with a low correlation coefficient. The multivariate function equation describing the relationship between fluid mud properties and sound velocity was constructed using the PCA-based 2-D eigenvalues, which for velocity inversion conform to a linear relation with the slope and intercept of 1.525~1.883 and 2.288~2.665, respectively.