Geotechnical property results from Deep Sea Drilling Project Hole 576A sediments represent the most complete data set ever compiled for a continuously depositional, sedimentary section that spans 65 m.y. Geotechnical analyses included index-property and sediment characterization, and consolidation, permeability, and triaxial testing. Excellent agreement exists between test data generated in this multilaboratory effort.Sediment characterization and index-property data delineate three well-defined units that conform with major lithologic divisions. Within Subunit IA these data appear inconsistent with accepted geotechnical relationships, showing water content, plasticity, and grain size increasing over similar intervals. These unusual relationships are attributed, in part, to silt-sized bonded clay aggregates. Within Subunit IB geotechnical properties become more uniform, and a marked increase in X-ray amorphous material occurs below 28 m sub-bottom. A pronounced change in the geotechnical behavior of Hole 576A sediments occurs in Unit II and corresponds to the presence of calcareous oozes.Consolidation test results show overconsolidated sediments in the upper 28 m and normally consolidated sediments between 28 and 55 m sub-bottom. Mechanisms to explain the state of overconsolidation that are consistent with the geological history of the area include cementation and interparticle bonding, the release of high hydrostatic pressures during core recovery, and artifacts resulting from the consolidation test process. Additionally, the relevance of the preconsolidation stress determined using consolidation test results may be limited.Variations in the shear strength gradient with depth are consistent with the consolidation test results. The gradient for the overconsolidated interval (0 and 28 m sub-bottom) is significantly higher than between 28 and 55 m sub-bottom, where the sediments become normally consolidated.

Supplement to: The Marine Geotechnical Consortium (1985): Geotechnical properties of Northwest Pacific pelagic clays: Deep Sea Drilling Project Leg 86, Hole 576A. In: Heath GR; Burckle LH; et al. (eds.), Initial Reports of the Deep Sea Drilling Project, Washington (U.S. Govt. Printing Office), 86, 723-758