horizontal posIHon; they were not packed to reduce the effects of vibration and 

 shock. 



Until tested all cores except those in metal barrels were stored upright at the 

 BUDOCKS soils laboratory in a room of about 98 percent relative humidity. 



B. SAMPLING PROBLEMS 



General statement — Two fundamental questions confront those who measure 

 shear strength in submarine sediment cores: (1) how is the thickness and depth of any 

 given stratum in a core related to its in-place thickness and depth, and (2) how much 

 disturbance to the sedimentary structure is caused by the sampling operation? Unfor- 

 tunately, neither question is easily answered. 



The gross recovery ratio (Hvorslev, 1949, p. TOO), Rg, defines the gross length 

 of core recovered, Lg, in terms of the depth penetrated by the corer, H . 



^9 = ^ (" 



A nearly sacrosanct assumption made by many marine geologists is that piston samplers 

 usually collect undisturbed samples with gross recovery ratios of 100 percent (see: 

 Kullenberg, 1947, p. 14; Ericson and Wollin, 1956, p. 107; Ewing, 1960, p. 191; 

 and Ericson and others, 1961, p. 196). Another common assumption is that core 

 shortening inevitably occurs in gravity cores and the gross recovery ratio is less than 

 100 percent. Recent investigations suggest that both assumptions are In need of 

 revision . 



Principles and mechanics of gravity and piston coring are considered In detail 

 elsewhere (Piggot, 1941; Hvorslev and Stetson, 1946, p. 938-943; Kullenberg, 1947, 

 p. 23-32, and 1955, p. 53-76; and Hvorslev, 1949, p. 93-110). Hence, our attention 

 immediately can be directed to the two principal problems stated above, following the 

 presentation of a few helpful ratios defined by Hvorslev (1949, p. 105-109) that effect 

 corer performance . 



The inside clearance ratio, C;, controls inside friction 



Ds - De 

 C. = \ ^ (2) 



where D^ is the minimum inside diameter of the core barrel or core liner and Dg is the 

 minimum inside diameter of the core nose (core cutter). Outside friction is controlled 



12 



