studies. The principal conclusion reached by these investigators was that reduction 

 of pore water salt content, or leaching, decreases the undisturbed shear strength of 

 clay and increases the sensitivity; although, Skempton and Northey (1952, p. 43) 

 found a reduction of the remolded strength but not of the undisturbed strength . It is 

 suggested that variability of submarine sediment sensitivity may be, at least in part, 

 explainable by changes in pore water salt content . Measurement of interstitial water 

 salinity is of importance, and it is to be regretted that so few measurements exist. 



In conclusion, natural marine sedimen^ predominantly composed of mineralogenous 

 matter, apparently has a cardhouse structure that will be rearranged into a parallel 

 orientation if disturbed by sampling for instance. It is hypothesized that rearrange- 

 ment may be directly proportional to the quantity of microskeletal remains in the fine- 

 grained fraction. A corollary of the hypothesis is that at about the same water content 

 sediments rich in microskeletons will tend to have lower sensitivities than those com- 

 posed entirely of clay minerals. Following structural rearrangement, a regain of 

 strength due to thixotropic hardening will occur with time . If the clay consists of an 

 ideal, purely thixotropic plastic material, the strength regain will be complete. 

 Skempton and Northey (1952, p. 35, 38) found that most natural clays were not 

 purely thixotropic materials . Furthermore, coarse-grained cohesive sediments, com- 

 posed of sand and possibly containing less than 5 percent clay minerals, possessing 

 thixotropy are mentioned by Mielenz and King (1955, p . 223) . It is probable that 

 most deep-sea sediments once disturbed likewise will not completely regain lost 

 strength . The answer to the question how much of the original strength in slightly 

 disturbed sediment cores will be regained over a specific time will have to wait 

 until less disturbed samples than those at present are collected, or until it proves 

 feasible to make in-place tests on the ocean floor. 



H. MODULUS OF ELASTICITY 



The modulus of elasticity is defined by the ASCE as the ratio of stress to strain 

 for a material under given loading conditions; it is numerically equal to the slope of 

 the tangent or the secant of a stress -strain curve. Values reported in Appendix B 

 were determined from results of the compressive strength tests; they range from 

 to 870 g/cm 2 (0 to 12.4 psi) . 



This modulus sometimes is used in settlement computations where deformation 

 occurs in accordance with Hooke's law (see, for instance, Skempton and Bjerrum, 

 1957, p. 169, who note that the modulus of elasticity — called Young's modulus — is 

 sensitive to sampling disturbance, especially in normally consolidated clays). Further 

 discussion of stress, strain, elasticity, and plasticity can be found in books on these 

 subjects (for example, Westergaard, 1952) and need not be considered here. 



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