Stress-Deformation Behavior of Two Carbonate Oozes

The geotechnical properties, including strength and compressibility, of two deep-sea carbonate ooze cores are discussed. The sediment samples were obtained from the vicinity of the Christmas and Fanning Islands in the Pacific. Both sediments consisted of fine sand- to silt-sized carbonate foraminiferal and nannofossil oozes with 88 to 93% calcium carbonate. The samples had high water contents (89 to 127%), exhibited some plasticity, and were very sensitive to disturbance and shaking.Results of consolidation tests indicate apparent overconsolidation behavior. The resistance to deformation caused by prolonged sustained loads was studied by running long-duration consolidation tests. It was found that significant secondary compression occurred under sustained stress (C _α = 0.03 to 0.05), and that the sediment developed resistance against further compression. From this, it is postulated that the in situ compressibilities are likely to be lower than those measured in the laboratory by standard consolidation tests (C _c . = 0.67 to 0.91).Undrained strengths were 11 to 12 kPa, and the samples exhibited sensitivities in the range of 6 to 10. In terms of effective stress, the behavior was typical of slightly overconsolidated deposits, with small c′ values, and φ′ values of 27 and 35°.