Strength and stress-strain behavior of clays from the nares abyssal plain

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The Nares Abyssal Plain is situated in the Western North Atlantic between 22° and 25° N and 60° and 67° W. This distal plain is connected to the Hatteras Abyssal Plain by the Vema Gap. The study site contains pelagic and hemipelagic sediments with upper meters containing predominantly finegrained turbidites. Large diameter piston cores up to 26 meters in length were obtained within the southern region of the Nares. This study focused on the stress-strain and strength properties of the pelagic clay units of the sediment column. A significant portion of the sediment column was found to be in a state of under-consolidation attributed to impeded drainage caused by apparent over consolidation of the surficial zone and significant variations in permeability between pelagic and turbiditic layers. Effective friction angles ranging from 19.9 to 31.6 degrees were generally higher for isotropically as opposed to anisotropically consolidated triaxial series. Additionally, there were correlations between friction angles and silt content. Stress-strain behavior for anisotropically consolidated samples illustrated brittle failures and low failure strains ranging from.7 to 4.2 percent. Isotropically consolidated samples revealed plastic type failures with failure strains ranging from 5.0 to 19.0 percent strain. Average horizontal to vertical effective stress ratios averaged from.57 to.59. An undrained vane shear strength profile ranged from 3 kPa at 2.0 m to 28 kPa at 25.7 m. Undrained shear strengths determined using triaxial parameters and plasticity indices were generally higher than the vane shear strengths. A critical state strength equation yielded strengths most compatible with the vane shear profile. © 1988 Taylor & Francis Group, LLC.

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Marine Geotechnology