Improved fixed-piston and gravity-type, thin-wall corers designed and built at the Norwegian Geotechnical Institute were used to sample localities selected by a sub-bottom, echo-sounding survey in an integrated geochemical, geological, geophysical, and geotechnical investigation of the Oslofjord. Changes in mass physical properties, particularly grain size and bulk density, were correlated with near-surface acoustic reflections from specific sub-bottom strata. Shear strength of the fine-grained, cohesive sediment was measured in the laboratory using the new Norwegian unconfined compression apparatus and the Swedish fall-cone. The latter instrument is of particular value for the scientific study of the strength of soft, Recent marine sediments because of the small amount o material necessary for a valid test. Natural strength was found to be strongly influenced by the remains of ploychaete burrows, the extent of which was demonstrated by radiography. Sediment sensitivities generally were medium to very sensitive, but in a few instances were quick. All material had normal fjord pore-water chlorinities (about 19^pmil), and the quick character of the clay appeared related to an abnormally high content of calcium carbonate. The sediments were underconsolidated above a depth of approximately one meter.

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