directly related to the wet unit weight (Fig. 8). A particularly clear example is shown 

 in the graph of core F 6, Plate XVII . At a depth of 208 to 248 cm (82 to 90 in), the 

 sand-size fraction decreases from about 37 to 25 percent. Particle specific gravity 

 decreases from a normal value of about 2.76 to 2.73 over this interval . 



Discussion — Few comparative values of the specific gravities of solids of deep- 

 sea sediments are available. Sykes (1960, p. 31) measured specific gravities, which 

 were not corrected for salt content, ranging from 2.78 to 2.83 in clay-size sediments. 



D. WET UNIT WEIGHT 



Procedure — It is appropriate to first remark that the term density as used in 

 physics rarely is used by soil engineers. Density, p, is defined as mass per unit volume, 

 while in soil mechanics unit weight, y, is defined as weight per unit volume. The two 

 terms are related by equating unit weight to the product of density and the accelera- 

 tion of gravity, g, (y = pg) . The reader is referred to soil mechanics texts (for example, 

 Hough, 1957, p. 27; Spangler, 1960, p. 55) for further discussion. 



Wet or mass unit weight, y , is defined as the weight per unit of total volume of 

 sediment mass, irrespective of the degree of saturation (ASCE), or 



Wo - W 



y = — (6) 



'my v ' 



where Wo is the weight of the sample plus container, W c is the weight of the container 

 alone, and V is the volume of sediment in the container. The degree or percentage of 

 saturation is the ratio of the volume of water in a given sediment mass to the total 

 volume of intergranular space or voids (ASCE); its determination is given by equation 

 16. Although wet unit weight is semantically correct, all samples at the time of test 

 were sufficiently close to 100 percent saturation to permit the use of the term saturated 

 unit weight, which represents the in-place unit weight or bulk density. Values are 

 reproducible only to . 1 because of the difficulty in eliminating very small voids 

 between the sample and cylinder wall with consequent loss of precision in the volu- 

 metric measurement „ 



Results — Values of wet unit weight range from a maximum of 1 .86 g/cm^ at 

 50.35 percent porosity in Area F to a minimum of 1 .23 g/cm^ at 86.4 percent porosity 

 in Area G. 



The straight -line relationship of wet unit weight to porosity (Fig. 8) previously has 

 been shown by Hamilton and Menard (1956, p. 760) and Nafe and Drake (1957, p. 542), 



20 



