data of this study well and is, therefore, suggested for use in analyzing 

 seafloor sediments of a similar nature. It should be noted, however, 

 that Ladd and Lambe present curves for soils other than Weald clay, and, 



although most (5 out of 8) of the curves are similar, several differ 

 significantly. Therefore, extrapolating these data to different mate- 

 rials (possible deep sea oozes and clays) may lead to error. Research 

 on these soils is needed and is currently in progress at NCEL. 



The data of Figure 6 are presented in numerical form in Table IX 

 so that a comparison of the different treatments and soil types can be 

 made. As can be seen, there are significant differences among the data, 

 and the following observations can be made: 



1. There is a strong variation in sample quality among the three 

 sites. The silty, slightly plastic soil of the 100-foot site yielded 

 laboratory strengths 40 to 50 percent lower than the in-situ values with 

 correspondingly low residual pore pressure ratios. The more plastic, 

 although equally coarse grained, samples from the 600-foot site were of 

 better quality (20 to 30 percent strength reduction), while the plastic, 

 clayey samples from the 1200-foot site were the highest in quality 

 (almost no strength reduction) . Some of this strength reduction is a 

 result of in-situ shear stress removal, which is completely unavoidable. 

 The extent of this disturbance is about 15 percent for the 100-foot site 

 soils (Beard, 1972) and probably somewhat less for the other more plastic 

 soils. One problem with the 1200-foot site is apparent: some of the 

 strengths are higher than the in-situ values and the residual pore pres- 

 sures are more negative than the reference pore pressures . This appears 

 almost certainly to be a result of either partial drying or partial 

 consolidation. Since the samples were well sealed, the possibility of 

 consolidation during the period of vertical storage appears more probable, 



2. The NCEL fixed piston and Lehigh gravity samples appear to be 

 almost identical in quality although the NCEL equipment has the advan- 

 tage of yielding longer cores. When subjected to standard practices, 

 the samples from both corers were of sufficient quality to produce 

 laboratory vane strengths within 30 percent of the field vane values 

 for the more plastic 600- and 1200-foot sites. These values may be 

 adequate for design without a disturbance correction. Both types of 

 samples of the less plastic 100-foot site soils were more disturbed, 

 with the amounts of disturbance almost identical for the two types of 

 corers. For soils such as those at the 100-foot site, disturbance 

 corrections would usually be required. 



3. Low frequency vibration did not produce a significant change 

 in the strength, although the residual pore pressure was less negative 

 than for standard treatment. 



4. High-frequency vibration caused large changes in residual pore 

 pressure (except for the possibly partially consolidated 1200-foot site 

 soils) with corresponding large changes in strength. 



5. Long-term and nonrefrigerated storage had pronounced effects 

 with average strength values on the order of 40 percent less than the 

 field values. 



22 



