The first correlation, Figure 28, involves a plot of sediment 

 strength versus increment depth. The plot shows a large scatter of 

 "strength per depth" for the abyssal plain sediments. The episodic 

 deposition of material seems to create a variety of strength values. 

 The deviations suggest that either the mineralogic composition varies 

 significantly during these events, or the particle arrangement differs 

 with different events. Although the scatter of data for pelagic material 

 is less, the results do not indicate a unique strength-versus-depth 

 profile for pelagic materials. Both sediment types appear to have a 

 finite value of strength at the soil-water interface. This value of 

 strength generally varies from 5 to 25 gm/cm^ at the soil-water inter- 

 face to approximately 37 gm/cm^ at a depth of 200 centimeters. 



The c/p ratios were compared to the plasticity indices in Figures 

 29 and 30. The c/p ratio theoretically removes the effects of overburden 

 pressure on the strength measurement. Once strength has been converted 

 to this form, it can be compared to various index properties that depend 

 upon the mineralogic characteristics of the material. Neither plot shows 

 any noticeable correlation between the normalized strength and index 

 properties. The scatter appears larger of the abyssal hill provinces. 

 The plots do indicate that the plasticity indices and the c/p ratios are 

 generally smaller for abyssal plain material. The c/p ratio exceeds four 

 more than half the time for abyssal hill materials, while the similar 

 ratio was usually less than four for abyssal plain materials. The minimum 

 values of c/p for the abyssal plain and abyssal hill data are 0.5 and 

 0.9, respectively. 



Similar plots , Figures 31 and 32, were used to compare the liquid 

 limit to the c/p ratio for abyssal hill and abyssal plain provinces. 

 Once again, the data from each plot were scattered. Since c/p varied 

 with depth, a third set of plots evaluated the behavior at given depth 

 increments (c/p versus liquid limit at 100-centimeter depth). Although 

 the scatter of points decreased, no usable correlation appeared, and, 

 therefore, the plots were not included. 



These series of correlations seem to define a unique property of 

 seafloor soils. In the upper 150 to 250 centimeters, the soil does not 

 have a constant value of c/p. The ratio decreases from infinity at the 

 surface to approximately 0.4 at the aforementioned depths. The values 

 of c/p vary widely in that depth range. The largest scatter occurs in 

 sediments of pelagic origin. It is, therefore, assumed that the magnitude 

 of intrinsic forces developed for surface sediments also varies signifi- 

 cantly. Since the indices are unable to distinguish any difference, the 

 function must depend on some time-dependent mechanism. 



Figures 33 and 34 compare the liquidity index to the sensitivity. 

 Although it was thought that the sensitivity would increase as the 

 liquidity index increased, no significant correlation appears. However, 

 it is interesting to note that the scatter of sensitivities for abyssal 

 hill sediments exceeds the scatter of sensitivities for abyssal plain 

 sediments. The average sensitivity of both materials is about 4.0, 

 Terzaghi and Peck (1968) define clays with sensitivities of about 4.0 

 as "insensitive to sensitive". 



36 



