This chapter summarizes the results of geotechnical measurements made on cores taken at the three deep ocean sites that have been studied in detail as part of the international programme assessing the feasibility of deep ocean disposal of heat generating radioactive waste. The capabilities of existing sampling methods and the adequacy of the available data for providing the geotechnical parameters needed to evaluate the technical feasibility of deep ocean disposal are discussed It is concluded that, while it has not been possible to obtain core samples of sufficient quality and depth to provide all the parameters needed for the assessment, no fundamental differences between the sediments at the study areas and those found on land or in shallow water have been identified
For the past five years an internationally coordinated programme of research has investigated the engineering aspects of the disposal of heat-generating waste (HGW) in deep ocean sediments At an early stage of the programme it was necessary to develop numerical models, for instance, to assess the penetrator embedment depths. Initially assumed geotechnical parameters were used based on experience with terrestrial sediments and the limited information available for deep ocean sediments.
During the programme three sites have been selected for detailed study namely
Great Meteor East (GME)
Southern Nares Abyssal Plan (SNAP)
West Pacific Study Area (PACl/E2)
These study areas are shown in Figs 1, 4 and 7 respectively
This chapter summarizes the capabilities of the coring methods used to obtain samples, and the geotechnical parameters required to characterize the sediments and evaluate the technical feasibility of disposal The results of geotechnical measurements made on cores from the three study areas are summarized.
Davie et al (1978) report three sources of ocean sediments
Pelagic sediments formed by dust particles and marine skeletons which settle out from the oceans
Turbidite sediments derived from deposits on the flanks of continental shelves and mid-ocean ridges, and transported to the deep ocean floor in turbidity currents caused by slope failures
Glacial erratics transported by icebergs
Pelagic sediments are predominantly silts and clays Those deposited above the carbonate compensation depth (CCD), the depth below which suspended calcium carbonate dissolves in the ocean, contain a high percentage of calcium carbonate Those deposited below the CCD are fine-grained and consist of clay minerals, principally illites and smectites.
Calcium carbonate occurs in the ocean as micro-fossils which are plankton skeletons The most common types are forarminifera (forams, between 100 and 500 microns) and nanofossils (coccoliths, between 2 and 10 microns) Both of these have open porous structures which contain water.
Turbidite sediments have variable grain size and carbonate content, depending on the deposits from which they originate Turbidite deposits near the source are coarser (generally sand and silt sized) than those deposited far from the source. Because turbidites are transported rapidly down-slope, they may have high calcium carbonate contents even when they are deposited below the CCD When turbidites are deposited, the silt and sand fraction settles rapidly to form a coarse-grained base.