IN-SITU GEOTECHNICAL CHARACTERIZATION OF SEDIMENTS OF THE NOVA SCOTIAN SLOPE, EASTERN CANADIAN CONTINENTAL-MARGIN

A seabed 2-m-long cone penetrometer and coring system (Geotechnical Mo dule) has been used at 17 stations in four transects on the Scotian Sl ope to characterise in situ shear strength and induced pore pressure o n several different types of late Pleistocene and early Holocene failu re. Study sites were selected using the SAR high-resolution deep-towed acoustic system equipped with a digital 160-190 kHz sidescan sonar an d a 3.5 kHz subbottom profiler. Several distinctive types of ''geotech nical signature'' were recognised from plots of cone resistance and in duced pore pressure with depth in the sediment. Normally consolidated sediments show a progressive increase in cone resistance with depth (t o about 75 kPa at 2 m subbottom). Holocene surficial muds show spectac ular apparent over-consolidation, reaching a peak of 250 kPa at about 50 cm subbottom and then decreasing down to 1.5 m. This overconsolidat ion is associated with Zoophycos burrows. Late Pleistocene sediments e xhumed by bedding plane slides show strong true overconsolidation cons istent with the original depth of burial inferred from high-resolution seismic stratigraphy. Debris flows show only a slight shear stress gr adient with depth (40-45 kPa over 0.5-1 m subbottom) with under-consol idation due to remoulding of sediment.