VI . SUMMARY AND CONCLUSIONS 



Thirty gravity and piston cores were collected from eight areas In the North 

 Atlantic, West Mediterranean, and Central Pacific. They were transported to the 

 laboratory in Washington, D. C., with protection against mechanical vibration and, 

 so far as possible, in an upright position. Sediments were composed of clayey sllt- 

 and sllty clay-sized particles, predominantly of terriginous origin. 



A knowledge of the gross core recovery ratio (gross core length/corer penetration 

 distance) is of Importance for engineering and other Investigations requiring sample 

 depth. Evidence Is presented from recent Swedish Investigations that this ratio may 

 not be always TOO percent for piston cores, as Is commonly assumed. The ratio Is 

 variable for gravity-type cores; it appears to be a function of the design. Well -engi- 

 neered gravity corers have gross recovery ratios about 100 percent In the upper 40 to 

 75 cm and smaller ratios below this depth. Poorly-engineered (for undisturbed sam- 

 pling) gravity corers may have core shortening proportional to the distance penetrated 

 and gross recovery ratios much less than TOO percent. 



Ail gravity and piston cores In general use by oceanographers appear to take 

 disturbed samples; disturbance is worse In some than In others. Better designed sam- 

 plers or In-place tests, perhaps by neutron probe or from deep submerslbles, are 

 required for more valid strength measurements. 



Sediments described In this report are considered to be disturbed, the principal 

 cause of which Is sample collection because proper care was exercised elsewhere to 

 protect against major disturbance. A quantitative figure for the reduction of In-place 

 strength Is unknown, but the amount Is believed sufficiently small to allow the use of 

 the strength values reported for most engineering purposes. 



Shear strength, expressed as cohesion, was measured In the laboratory by com- 

 pression and vane tests that are briefly described. Most cores were continuously 

 sampled and measured for cohesion every 5 or 10 cm. 



Cohesion, graphically related to depth for each core, usually increases with 

 increasing depth. This Increase In some Instances Is regular and In others highly ir- 

 regular. A few cores possessed a relatively uniform strength distribution from top to 

 bottom . The least cohesion measured was 4.2 g/cm^ and the greatest 234 g/cm''. 

 Most cores showed minimum cohesion at the top and maximum values at intermediate 

 depths . 



Sediment sensitivity ranged from 1 .6 to 26, with most values falling between 2 

 and 6, medium to very sensitive. It Is speculated that in-place sensitivity In many 



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