Strength and consolidation properties of surficial sediments, Flemish Pass: effects of biological processes

Abstract

The upper 50 cm of surficial sediment from 1145 m water depth in Flemish Pass, off eastern Canada, was sampled by box corer. The sand content of the sediment increased from 5% to almost 25% at 50 cm depth, which radiocarbon dating of mollusc shells indicates is about 2.5 ka. Packed mud tubes of Maldaniid polychaetes were abundant in the upper few decimeters of sediment whereas they appear to have disintegrated deeper in the section. Sponge spicules were particularly abundant in the uppermost 20 cm. The undrained shear strength of both the bulk sediment and intact Maldaniid worm tubes was measured with a miniature vane shear device and a Swedish fall cone, which revealed that unusually high strengths existed within the worm tubes themselves. Back-pressured incremental consolidation tests clearly showed the box-cored sediment to be in a state of apparent overconsolidation, partly due to brittle yielding of a loose sediment framework composed mainly of interlocked sponge spicules. Surficial Flemish Pass sediments were highly compressible in one-dimensional consolidation testing. Bonding effects within the agglomerations of Maldaniid fecal material appeared to play a role in developing high yield and undrained shear strengths, but represent a transitional stage preceding burial and gravitational consolidation.