Geotechnical properties of ocean sediments recovered with the Giant Piston Corer: Blake-Bahama Outer Ridge

Consolidation tests were conducted on sediment samples from four cores (17-31 m lengths) obtained with the Giant Piston Corer on the Blake-Bahama Outer Ridge (water depths 4758-4962 m). Three of the cores (GPC-7, 8, 9) had similar composition (calcareous lutites) and texture (60% clay) and similar vertical variability in water content, shear strength and carbonate profiles with very large decreases in water content (average decrease of 52%) occurring at 20 m depth. The fourth core (GPC-11) has considerable sand- and silt-sized material (calcareous tests) and much higher shear strength. The consolidation results of core GPC-11 showed a significant amount of overconsolidation suggesting that more than 10 m of sediment has been eroded and that the core was taken in the bottom of a large erosional furrow. Correlations between consolidation parameters and composition are proposed through use of a mineralogy factor (E) such that the mineralogy of the clay fraction is combined with effects of stress history and clay fraction influence as follows:. E=[(M* + I) - (%CaCo3)] × [(w0 - wp) %\u3c2μm]. where: • M* = percentage of montmorillonite plus mixed-layer montmorillonite-illite, • I = percentage of illite, • w0 = in-situ water content, and • wP = plastic limit. The following regression-line equations were obtained based on consolidation test results from Blake-Bahama Outer Ridge:. Compression Index = Cc = 0.0162E - 0.0333. Coef. of Secondary Compression = C∝ = (0.461E - 0.126) · 10-3. Although clay mineralogy does have an effect on consolidation behavior, the effects of consistency coupled with percentage of calcium carbonate exert the greatest influence on the consolidation characteristics of these sediments. © 1979