Geotechnical Studies in the Baltimore Canyon Trough Area

ABSTRACT The results of a site investigation, onshore laboratory testing program and interpretation of data from the standpoint of application and hazard are presented in this paper. The study site was generally between the Atlantic OCS exploration leases in the Baltimore Canyon Trough ana potential markets on the eastern US coast. Twenty vibrocores were collected from the R/V Annandale with penetrations of approximately 5 meters into sandy and clayey sediments These cores were subjected to a comprehensive geotechnical engineering test program including consolidation-compression and triaxial tests as well as identification and classification tests. Geologic studies of these cores and other data from the area established a regional setting for the specific test results. The studies reported in this paper were done by the U.S. Geological Survey for the U.S. Bureau of Land Management with particular concern for evaluating potential geologic hazards or engineering constraints. However the results have more general regional application to geotechnical engineering problems. Since the depth of sampling was limited, the results are particularly applicable to bottom supported communication structures, such as pipelines and cables, sea bottom trafficability, shallow excavation, lightweight structures and several types of natural hazards. The conclusions of this study indicate that the shallow marine sediments from the Baltimore Canyon Trough corridor area are more or less typical of terrestrial soils from adjacent shore areas. Extensive deposits of sand, some being loose and mobile, are described. The clay sediments are predominently overconsolidated with adequate shearing resistance and low compressibility. Some local deposits of weak and compressible, sediments were found. The hazard implications of these studies are systematically reviewed. INTRODUCTION Potential for future development on the Atlantic Outer Continental Shelf (OCS) requires that the U.S. Bureau of Land Management anticipate where development may be proposed and conduct appropriate studies. These studies include those by the U.S. Geological Survey that are concerned with the evaluation of geological hazards. Current interest and activity in the Atlantic OCS centers on exploration drilling in the Baltimore Canyon Trough area. In addition to the drilling locale itself, the routes for communication between the drilling sites and shoreline facilities should be studied. If commercial quantities of oil or gas are discovered in the Baltimore Canyon Trough area, transport to shore will most likely be through pipelines supported in or on the sea bottom. This study is concerned with evaluating the engineering characteristics of the sediments and any potential hazards within a representative transect across the Continental Shelf in the Baltimore Canyon Trough area. To collect specific information for the study, a cruise was conducted by the U.S. Geological Survey using the R/V ANNANDALE during 18–25 September 1977. During the cruise, 20 vibracores were collected at 17 stations across the shelf in water depths of 35 to 70m (Figure 1). Immediately after the cruise the cores were taken to the laboratories of Geotechnical Engineers, Inc. of Winchester, Massachusetts. There, an extensive series of geotechnical engineering tests was carried out on the cores; these data are the basis of this report.