Abstract

Piston cores and high-resolution seismic reflection data were collected on the upper continental slope in the Baltimore Canyon DCS Lease Sale 59 area by the U.S. Geological Survey during September 1979 to obtain information on the stability of near-surface sediments in a variety of locations on valley axes, valley walls, and internally ridges in water depths ranging from 328 to 1342m.

The stability of 31 sites was examined in terms of the infinite-slope stability model using geotechnical profiles of the sites, together with sea-floor gradients interpreted from geophysical and bathymetric data. The geotechnical profiles include information obtained from the piston cores on the physical properties of the materials, their consolidation states, and their drained and untrained shear strengths in terms of normalized soil parameters.

The majority of the sites contained over consolidated, materials, and their safety factors generally exceeded 2.0 for both drained and untrained conditions. Under consolidated materials were found in about one-third of the sites. Among these, low safety factors for untrained conditions (on the order of 1.0 or less) were obtained at five sites where sea-floor gradients were on the order of 150 or greater. Four of these sites were on valley walls, and one was on an internally ridge.

Compared with previously reported geotechnical information on near-surface Atlantic slope sediments, the materials in this study have a limited range of plasticity characteristics, but a similar range of consolidation states and shear strengths. Moreover, variability in the latter occurs on a more local scale than variations in the morphology of the continental slope

Introduction

This paper describes a geotechnical study of the stability of near-surface sediment on the mid-Atlantic upper continental slope that was undertaken to assist the U.S. Geological Survey (USGS) in its assessment of potential geologic hazards and constraints for selected lease blocks in the Outer Continental Shelf (OCS) Lea, Sale 59 area1,2.

This study is based on piston cores and high resolution seismic-reflection data collected from 31 sites by the USGS during September 1979. Laboratory analyses on the piston cores were used to interpret, for each site, a geotechnical profile of the physical properties of the materials, their consolidation state, and their shear strength under both drained and untrained conditions. Sea-floor gradients were defined from the seismic reflection profiles and existing bathymetric data. The stability of each site was calculated from the above using the infinite-slope stability model.

The regional significance of the results is examined with regard to the location and geomorphic setting of each site, and in relation to previously reported geotechnical information for near-surface sediment on the Atlantic continental slope.

Setting

The study area is on the continental slope seaward of New Jersey and Delaware in the Baltimore Canyon trough area (Fig. 1). The sites were located in the region of the upper and middle continental slope from Baltimore Canyon to Mey Canyon, and in water depths ranging from 328 to 1342 m.

The topography of the mid-Atlantic continental slope is dominated by numerous down slope trending valleys and a dendrite pattern of gullies on the valley walls that feed into the Val eys3, 4, 5.

This content is only available via PDF.
You can access this article if you purchase or spend a download.