Permeability of deep-sea clays: Northwestern Atlantic

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Permeability characteristics of deep-sea sediments from the East Bermuda Rise and Blake Bahama Outer Ridge areas of the northwestern Atlantic were investigated. The samples were predominantly clay sized, although there were significant percentages of coarser-grained material. The coefficients of permeability were directly measured by imposing a hydraulic head across the sample and were calculated according to the theory of one-dimensional consolidation. Darcy’s measured coefficients of permeability ranged from 7.93 ts 10-7 cm/sec at a void ratio of 3.66 to 1.10 ts 10-8 cm/sec at a void ratio of 1.10. Of the two methods (log of time and square root of time) the square root of time method agreed more with the measured permeability values. This is related to the square root of time’s reliance on the earlier stages of consolidation, when the excess pore pressures across the sample are greater and secondary effects are reduced. Existing theory based on the physiochemical nature of the clays was inadequate (for predicting the coefficient of permeability). The measured values generally exceeded those predicted by the theory. Previously proposed modifications to the theory, which account for the formation of particle flocs or clusters within the sample, overcompensate, and the measured values of the coefficient of permeability are less than predicted by the modified theory. Another modification is proposed that accounts for the integrated sediment matrix of coarse and fine-grained material within the sample. © 1982 Taylor & Francis Group, LLC.

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Marine Geotechnology