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New miniaturized in-situ geotechnical instruments have been developed and field tested with the DSRV Alvin in various sedimentary features associated with mass movements of sediments on the U.S. East Coast slope and rise within the Wilmington geotechnical corridor. The instruments include a cone penetrometer, resistivity probe, miniature piezometer, and an inclinometer.
The penetrometer produced a continuous profile of sediment cone resistance and was useful in determining recent sediment thicknesses to 1.3 m at several sites. The resistivity probe produced a continuous profile of sediment electrical resistance/conductivity, which is related to sediment wet unit weight and porosity when pore water salinities, temperatures, and average grain densities are constant. The miniature piezometer is a prototype 8-mm diameter probe which measures sediment excess pore water pressures and the dissipation of pressures induced during insertion at various depths below the sediment-water interface. An inclinometer was also mounted on the submarine and continuously measured the sediment slope as the submersible traversed the sea floor.
The use of in-situ geotechnical instruments with a manned submersible provides the opportunity to select sites for detailed geotechnical analysis of specific sea-floor features such as previously slumped blocks, their slump scars, and sediment gravity flow deposits. Although depth of penetration of the submersible-mounted probes is limited to ~1.3 m, valuable detailed in-situ geotechnical data were obtained.
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