In situ measurements of sediment compressional and shear wave properties in Currituck Sound

Abstract

This paper reports in situ measurements of compressional and shear wave speed and attenuation collected below the sediment-water interface in Currituck Sound, North Carolina. Three measurement locations having distinctly different sediment types will be presented: (1) a near shore site with coarse sand, (2) a shallow-water site with silty fine-grained sand, and (3) an offshore site with loamy clay. At each site, grab samples were collected and later analyzed in the laboratory to quantify physical properties of the sediment, including grain size, density, and porosity. The in situ acoustic data were acquired using two measurement systems, each consisting of four probes mounted on a rigid frame. The shear wave system consisted of bimorph elements to generate and receive horizontally polarized shear waves; the compressional wave system was composed of cylindrically shaped piezoelectric elements. Both systems were manually inserted into the sediment, and waveforms were recorded by shipboard equipment. The measured wave speeds and attentions are compared to predicted values from one or more sediment models using the measured physical properties as inputs. The Biot-Stoll model, grain-shearing theory, Mallock-Wood equation, and card-house theory are considered for this analysis. [Work supported by ERDC, ARL:UT, and ONR.]