In-situ Measurements of Geotechnical and Geo-Acoustic Seabed Properties Using a Free Fall Cone Penetrometer

The FFCPT is a free fall probe that has been developed to measure acceleration and dynamic sediment porewater pressure as a function of depth of penetration into the seafloor. It also records hydrostatic pressure and optical backscatter in the water column, for mudline detection capability. This combination of sensors permits the direct application of geotechnical analysis methods and parametric-based correlations already long established in engineering practice. The FFCPT provides two independent means of calculating the undrained shear strength, as well as other engineering variables that are used in sediment textural classification. Specifically, there are accepted empirical relationships between the dynamic pore pressure parameter, the normalized dynamic penetration resistance and sediment grain size characteristics. The probe has a modular design allowing additional sensor payloads to be integrated. The first module to be developed measures resistivity, as a means to determine sediment bulk density. Experimental results from the New Jersey Strataform area and the Scotian Shelf will be presented and compared with measurements using a Seabed Terminal Impact Newton Gradiometer (STING) and an eXpendable Bottom Penetrometer (XBP).