few tens of g/cm-% and that undisturbed sediment at the liquid limit has a strength 

 about an order of magnitude greater . 



A quantitative measure of the plastic characteristics of a completely remolded 

 sediment is afforded by computation of the plasticity index, which defines the range 

 of water content in which sediment is plastic . Most of the predominantly inorganic 

 sediments of terrigenous origin and one core of calcareous clayey silt possessed high 

 plasticity (values located above the A-llne on the plasticity chart with the liquid 

 limits greater than 50 percent). 



Shear strength Is expressed as cohesion because tests were made on water-saturated, 

 fine-grained cohesive sediments without change in water content during the tests. Co- 

 hesion ranged from 4.2 to 234 g/cm2. Minimum values usually occur at the surface and 

 maximum values at some depth other than at the bottom of the cores. An average of 

 surface, to 5 cm, measurements is about 20 g/cm^ in predominantly terrigenous sedi- 

 ments and about 40 g/cm^ in calcareous sediments. 



In a given sedimentary environment, wet unit weight generally was directly pro- 

 portional to porosity and inversely related to cohesion. Median diameter, the sand- 

 or clay-size fraction, and plasticity index sometimes showed direct and sometimes an 

 inverse relation to cohesion. 



Further confirmation is given the (usually straight-line) relationship between 

 porosity and the logarithm of cohesion. Comparison of the different axial slopes on 

 porosity-logarithm of cohesion plots of each of the 8 areas suggests almost the same 

 relationship of relative deposition rates found in graphs of porosity as a function of 

 the clay-size fraction, although the porosity-logarithm of cohesion slopes are nega- 

 tive. Cohesion was found to have a variable relationship to the clay-size fraction. 



It is a well-known fact that the logarithm of cohesion is closely related to water 

 content. This indicates that a simple means of rapidly making a large number of shear 

 strength measurements in suitable laboratory samples, or in-place on the sea floor, 

 would be by measurement of the water content using a neutron probe that has been 

 calibrated for the water content-strength relationship of the particular sediments under 

 investigation . 



Measurements of sensitivity by compression and vane tests show that porosity may 

 be directly related to sensitivity, although there is a very large scatter of values about 

 the suggested average. The liquidity index has been considered by others to be a 

 measure of sensitivity. This generally is confirmed in the samples tested if each area 

 is considered separately and correlation lines are forced through the origin; otherwise 

 there does not appear to be a clear correlation between these two parameters. 



55 



