Mechanical properties of the sediment-Water interface

The hardness of marine sediments in the near-shore waters of Long Island Sound has been measured by penetration tests made both in situ and in the laboratory. Penetration of the sediment-water interface is found to be rate-insensitive and, for a given driving stress, independent of indentor size. Natural sediments in Long Island Sound show no measurable surface cohesion because of the effects of benthic animals, though artificial, azoic sediments prepared in the laboratory do. Hardness of marine mud is found to be sensitive to sand content. Analysis of penetration experiments in terms of punching a rigid-plastic material cannot account for these observations, but a model based on a description of the sediment as a locking material is successful. The observations are applied to defining the bearing capacity of the bottom and its resistance to burrowing by marine animals.