STRATIGRAPHY OF THE DEEP-SEA FLOOR 55 



water around the grains (Taylor, 1948, and others). When the 

 rate of load appHcation is very slow, Taylor (1948) and Laughton 

 (1957) thought it possible that minute loads would cause almost 

 no excess porewater pressure and consolidation,* therefore, will be 

 almost entirely secondary. It would appear that the extremely 

 slow deposition on the deep-sea floor, resulting in minute load 

 applications, would cause no excess porewater pressure. 



Consolidation Testing 



The consolidation behavior of a clay is studied by running a 

 consolidation test in the laboratory on relatively undisturbed 

 samples and on remolded samples of the same sediment. The sedi- 

 ment is placed in a ring with porous discs at top and bottom. A 

 load is applied to the top disc, and the water is permitted to flow 

 through the discs until deformation of the sediment has practically 

 ceased. The amount of deformation is measured on a dial gage. 

 When the rate of deformation becomes very small, a new load 

 increment is added. The results of such a test arc plotted as the 

 void ratio, e, (volume of voids divided by the volume of solids) 

 versus the corresponding total pressure, p. When plotted on semi- 

 logarithmic paper the curve is called, in soil mechanics, an e-\og p 

 curve and is used in the analysis of settlement which might be ex- 

 pected under given design loads. 



After overburden and other load pressures are computed for an 

 actual condition, one can enter the ^-log p plot along the pressure 

 line and pick off the corresponding void ratio for the particular 

 pressure. When examining a number of e-\og p plots for clay one 

 is struck by a very significant and important fact : no matter how 

 porous the original material, by the time that it is under about 

 100 kg/cm^ of pressure the void ratio has usually decreased to 



* The term "consolidation" is used in soil mechanics to refer to a process and 

 not to the solidity of material, which is the geologic usage. It is possible for a mate- 

 rial to be completely consolidated (under a certain load, or overburden) and still 

 be relatively soft. "Lithified sediment" is probably a better term to indicate that 

 a sediment has been cemented into a rock. In engineering parlance "compaction" 

 is reserved for artificial reduction of pore space, as with a sheep's-foot roller. 



