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    Bulk Density and Shear Strength of Several Deep-Sea Calcareous Sediments

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    Deep-sea calcareous sediment commonly consists of chemically active, fragile, biologically derived sand- or silt-size carbonate particles combined with terrigenous silt and clay and biologically derived opaline silica. The shearing strength of these sediments depends on whether the noncarbonate matrix or a carbonate framework dominates and on the physical nature of the noncarbonate matrix. A model based on relations between bulk density and carbonate content is developed to delineate three types of behavior: matrix dominant, transition, and carbonate-framework dominant. The model is quantitatively evaluated using vane shear, bulk density, grain density, carbonate content, and triaxial shear strength measurements from four studies of deep-sea calcareous sediments. The divisions between the three behavior types are found to be determined primarily by the character of the noncarbonate matrix. The presence or absence of opaline silica in the noncarbonate fraction has the strongest influence and is related to the overall sedimentary environment. Vane shearing strength increases with carbonate content through the transition and carbonate-framework-dominant zones. It is independent of carbonate content in the matrix-dominant zone. This trend may be masked by coring disturbance if only the results of laboratory analyses as opposed to in situ tests are considered. The cause of the strength increase with carbonate content may be the granular nature of the carbonate particles (mechanical) or interparticle cementation (chemical).


    calcareous soil, sediment, deep sea, marine geology, soil mechanics, geotechnology, shear strength

    Author Information:

    Lee, HJ
    Research civil engineer, U.S. Geological Survey, Menlo Park, Calif.

    Committee/Subcommittee: D18.05

    DOI: 10.1520/STP28910S