laboratory. This topic is currently being debated, and data are avail- 

 able to support almost any point of view. In this report it will be 

 assumed that laboratory consolidation does approximately represent 

 field sedimentation. Additional information on this subject will be 

 obtained during a later phase of this project, and modifications to 

 the conclusions of this report will be presented in subsequent reports, 

 if necessary. 



Four one-dimensional consolidation tests were conducted on speci- 

 mens taken from the two box cores. Two tests were performed using a 

 back-pressuring system (Anteus consolidometer) to increase saturation, 

 and two were performed without back-pressure. No significant differ- 

 ence between the results of the two types of tests could be detected, 

 thereby indicating that the samples were well saturated before testing. 



The results of the tests are shown in Figure 4 in the form of the 

 usual plot of void ratio versus the applied vertical effective stress. 

 Three of the tests were performed on specimens from Box A and yielded 

 almost identical results. Therefore, one average curve is presented 

 for this box. Also shown on this figure are estimated "maximum past 

 pressures" and estimated undisturbed consolidation curves. 



The maximum past pressure, determined using the Casagrande (1936) 

 technique, usually represents the maximum overburden pressure to which 

 a soil has been subjected at some time in the past. For these pelagic 

 clays the maximum past pressure is high (3.5 - 4.5 psi) relative to the 

 current in-situ overburden stresses (0 - .3 psi). This could indicate 

 a high degree of overconsolidation, produced perhaps by a scouring 

 away of 20 to 30 feet of material. However, such a situation could 

 also result from the development of relatively strong interparticle 

 bonds near the sediment surface as a result of electrostatic or long- 

 term factors. With no past embedment in excess of the current embed- 

 ment, such a situation would be referred to as pseudo-overconsolidation. 

 Whatever the cause of the behavior, the engineering applications of the 

 results are approximately the same. The important aspect is that the 

 material appears "overconsolidated" and as a result is much less com- 

 pressible and, as will be seen, stronger than would be expected for a 

 "normally consolidated" soil near the seafloor. 



Estimated, undisturbed consolidation curves were constructed using 

 the Schmertmann (1955) technique which was also used in the first re- 

 port of this series (Lee, 1973a). The relatively close correlation 

 between the undisturbed and laboratory consolidation curves is an in- 

 dication of the high quality of the box core samples. 



The usual static parameters obtained from these consolidation 

 tests are given in Table II. The two compression indices (change in 

 void ratio per one log cycle change in pressure) relate to whether the 

 applied pressure is less than or greater than the "maximum past 

 pressure." If it is less ("recompression"), the soil is almost 

 incompressible. If it is greater (virgin compression) , the soil be- 

 comes highly compressible. Obviously, engineering structures should 

 be designed to apply pressures below the "maximum past pressure," if 

 possible. 



