Parameter estimation errors in Buckingham's grain shearing model

A compilation of 54 sets of geoacoustic measurements of marine sediments was reviewed in order to bound estimates of parameters for use in Buckingham's grain shearing (GS) theory of acoustic propagation. These data, for unconsolidated sands (siliciclastic and carbonate) with grain sizes between 0.0156 mm and 0.57 mm, were all made in shallow water (maximum depth of 60 m) sites at diverse locales. In each data set, measurements of the speed and attenuation of the compressional wave at high frequency, the shear wave speed at 1 kHz, porosity, and bulk density are sufficient to calculate the three free parameters in GS theory (a material exponent, a compressional coefficient and a shear coefficient). The spread of the values calculated for GS parameters, combined with a sensitivity analysis, do not support the use of a single material exponent value for all sediments. Nor do they support the notion that the material exponent be 1, which would be the case if elastic and viscous forces at grain contacts are equal. Finally, it is suggested that, given the sensitivity to spot measurements, the GS parameters be estimated simultaneously from a full range of compressional and shear wave measurements.