Twenty-seven laboratory consolidation tests were made on predominantly silty-clay sediments from eight Atlantic cores, two Mediterranean cores, and two Pacific cores from the continental slope, rise, and deep-sea floor. Values of the coefficient of consolidation, determined over the pressure ranges of 0-0.05 and 8-16 kg./cm.², ranged from 2 × 10^-4 cm.²/sec. for the lower pressures to 34 × 10^-4 cm.²/sec. for the higher pressures. Compression indices computed from the relationship of the void ratio to the logarithm of pressure (e log p) ranged from 0.3 to 1.5.

Results of these tests show that the strength characteristics of sea-floor sediments are dependent upon the environments of deposition. Deep-water sediments generally are stronger than expected (they are "overconsolidated"). Evidence supporting this generalization, in addition to the consolidation data, is demonstrated by (1) the computed ratio of shear strength to effective overburden-pressure values (c/p) of about one to four, which are appreciably higher than the normal values of 0.2-0.4, and (2) the relatively small reduction of porosity with increasing depth below the water-sediment interface in homogenous sediment. The explanation for the observed relationship of deep-sea sediments exhibiting characteristics of overconsolidation is found in the very slow rates of deposition, gre t age, and the presence of appreciable amounts of clay minerals, volcanic detritus, and siliceous (Radiolaria) and calcareous (Foraminifera) biogenous matter. It is postulated that solutions of these materials in the sediments may yield iron, manganese, silica, and calcium carbonate that, together with the clay minerals, result in a kind of interparticle bonding having the effect of cementation, although actual cementation is not visible. These cementation effects are believed to be the cause of strengths greater than those expected.

End_of_Article - Last_Page 616------------