Geotechnical properties of shelf sdiments from the Prydz Bay

This paper presents a geotechnical characterization of the glacigenic sediments in Prydz Bay, East Antarctica, based on the shipboard physical properties data obtained during Leg 119, combined with results of land-based analyses of 24 whole-round core samples. Main emphasis is placed on the land-based studies, which included oedometer consolidation tests, triaxial and simple shear tests for undrained shear strength, permeability tests in oedometer and triaxial cell, Atterberg limits, and grain-size analyses. The bulk of the tested sediments comprise overconsolidated diamictites of a relatively uniform lithology. The overconsolidation results from a combination of glacial loading and sediment overburden subsequently removed by extensive glacial erosion of the shelf. This leads to downhole profiles of physical properties that have been observed not to change as a function of the thickness of present overburden. A number of fluctuations in the parameters shows a relatively systematic trend and most likely results from changes in the proximity to the ice sheet grounding line in response to variations in the glacial regime. Very low permeabilities mainly result from high preconsolidation stresses (Pc'). Pc' values up to 10,000 kPa were estimated from the oedometer tests, and empirical estimates based on undrained shear strengths (up to 2500 kPa) indicate that the oedometer results are conservative. The diamictites generally classify as inactive, of low to medium plasticity, and they consolidate with little deformation, even when subjected to great stresses. This is the first report of geotechnical data from deep boreholes on the Antarctic continental shelf, but material of similar character can also be expected in other areas around the Antarctic.