Examining the effects of microstructure on geoacoustic parameters in fine-grained sediments

This paper presents a set of controlled laboratory experiments designed to develop a basis for understanding the relationship between microscopic and macroscopic properties of fine-grained sediments. Two samples of kaolinite platelets were selected for this study, and effects of sediment microstructure on geoacoustic properties are deduced from a comparison of the measured properties. To provide additional interpretation of the acoustic measurements, compressional and shear wave properties are compared to predicted values from sediment-acoustic models. First, the shear wave speed was compared to predictions from card-house theory, a model with an electrochemical basis that incorporates the aggregation of clay platelets. The wave speed predicted by card-house theory showed good agreement with the measured wave speeds for the mud sample made up of card-house flocs. Next, viscous grain shearing theory, which treats unconsolidated sediments as a two-phase medium with internal losses arising from grain-to-grain contacts, was applied to predict the frequency dispersion of all four geoacoustic parameters. Overall, good agreement between the measurements and values calculated by viscous grain shearing theory was observed for both samples of mud.