IV. Conclusions 

 The relative merits of both tests are compared below. 



Factor 



Rigidense 



Atterberg 



Applicability 



Applies to total sample 



Applies only to that 

 portion of sample with 

 grain size U20 microns 



Applies only to samples Applies to samples taken 

 taken with coring devices with any type sampling 



device . 



Controllability 

 Reproducibility 

 Speed 



Applies to samples with 

 natural water content, re- 

 tained (for valid inter- 

 pretation) 



Less difficult 



More accurate 



Fast 



Applies to all samples 

 (water content may be 

 varied) 



More difficult 

 Less accurate 

 Slow 



Emphasis may be placed on the fact that the rigidense test applies 

 to the total sample and as such is a more accurate measure of the com- 

 paction and bearing capacity of the sediment* On the other hand the 

 primary shortcomings of the rigidense test are its dependence upon a 

 sediment sample having natural water content for valid interpretation 

 of test data and the fact that it may be applied only to cores. This 

 investigation does not deal with the underlying causes for the results 

 obtained. To do so would require a prohibitive number of man-hours 

 and extremely elaborate equipment. Instead, an attempt was made to 

 determine whether the faster rigidense method could replace the cumber- 

 some Atterberg tests « It is well to remember that there is probably 

 no substitute for an in situ measure of plasticity or penetration. 

 However, at the present time no device for making such a measurement 

 exists. Therefore, it is concluded that, as a relative measure of 

 plasticity and penetration in the laboratory, the rigidense test is 

 adequate and superior to the Atterberg tests. Samples which do not 

 have natural water contents should be run through a range of rigidense 

 measurements varying from low to high water content. Rigidense core 

 analysis has been made a standard laboratory procedure at the Hydro- 

 graphic Office • 



It remains for a future investigation to determine what the 

 relationship is between any laboratory measure of penetration and the 

 actual penetration of static or dynamic loads placed on the ocean bottom. 



