GEOTECHNICAL PROPERTIES OF NORTHWEST PACIFIC PELAGIC CLAYS - DEEP-SEADRILLING PROJECT LEG-86, HOLE-576A (REPRINTED FROM INITIAL REPORTS OFTHE DEEP SEA DRILLING PROJECT, VOL 86, 1985)

Geotechnical property results from Deep Sea Drilling Project Hole 576A sediments represent the most complete data set ever compiled for a co ntinuously depositional! sedimentary section that spans 65 m.y. Geotec hnical analyses included index-property and sediment characterization, and consolidation, permeability, and triaxial testing. Excellent agre ement exists between test data generated in this multilaboratory effor t. Sediment characterization and index-property data delineate three w ell-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 incre asing over similar intervals. These unusual relationships are attribut ed in part, to silt-sized bonded clay aggregates. Within Subunit IB ge otechnical properties become more uniform, and a marked increase in X- ray amorphous material occurs below 28 m sub-bottom. A pronounced chan ge 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 nor mally consolidated sediments between 28 and 55 m sub-bottom. Mechanism s to explain the state of overconsolidation that are consistent with t he geological history of the area include cementation and interparticl e bonding, the release of high hydrostatic pressures during core recov ery, and artifacts resulting from the consolidation test process. Addi tionally, the relevance of the preconsolidation stress determined usin g consolidation test results may be limited.