the development of high holding capacities. The relatively high 

 strength soil near the surface can consume a large part of a penetrating 

 anchor's kinetic energy. Unfortunately, since the strength increases 

 very slowly with depth, a great penetration is needed to obtain even a 

 moderate holding capacity. It may be necessary to downgrade the rated 

 holding capacities of direct embedment anchors when they are being used 

 in pelagic clays. 



Correlation with Index Properties 



One of the major goals of the current research is to derive corre- 

 lations between index and engineering properties so that designs can be 

 developed on the basis of tests on disturbed samples. Much of the data 

 of this report will eventually be incorporated into such correlations 

 and presented in a final report. For current purposes, however, only 

 one correlation was tried. Lambe and Whitman (1969, p. 452) present a 

 correlation between the ratio of undrained shear strength to overburden 

 pressures (S u /o vo ) and the plasticity index for marine clays. An esti- 

 mate of this ratio was obtained using the triaxial test results, and 

 Equation (3) and was found to correlate with the plasticity index in 

 almost exactly the same manner (within 5 percent) as the Lambe and 

 Whitman plot. However, this correlation was found to be valid for only 

 the clearly normally consolidated region (sub-bottom depths greater 

 than 50 feet) . For more shallow embedments , a more complex relationship 

 is needed. The ratio of strength to overburden pressure for depths 

 greater than 50 feet was found to be about 0.32, a typical value for 

 cohesive soils. 



CONCLUSIONS 



1. The index and engineering properties of two samples of pelagic clay 

 obtained from two difference locations were almost identical. 



2. The pelagic clay samples obtained from near the water-soil inter- 

 face display characteristics of overconsolidation. That is, the prop- 

 erties are similar to those of material that has been preloaded at 

 some time in the past. 



3. As a result of the apparent overconsolidation, the soil is almost 

 incompressible up to the apparent "maximum past pressure" of about 4 

 psi. The soil is very compressible beyond this point. Structural 

 loads in excess of this level should be avoided. 



4. The short-term strength of the pelagic clay samples from near the 

 soil-water interface is relatively high (about 1 psi) . This value is 

 higher than previously obtained strengths of more disturbed cores. 



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