6. Organic material decomposition was found to cause significant 

 disturbance. Samples stored without refrigeration for periods of time 

 ranging between one and six months changed color and developed strong 

 odors. The strength reduction was on the order of 25 percent but could 

 be evaluated using the residual pore pressure approach. 



7. Water content changes were most significant with cores stored 

 vertically. Well-sealed, horizontally stored cores appeared to main- 

 tain their water contents even when stored for as long as one year. 



8. Long-term storage did appear to affect the engineering properties 

 (40 percent vane strength reduction) , probably as a result of a creep 

 mechanism. The disturbance could be evaluated using residual pore 

 pressures . 



9. Core shortening was not investigated in this study. The two corers 

 used were designed to minimize this problem. 



CONCLUSIONS 



1. The rational design of foundations or anchorage systems for seafloor 

 installations requires a knowledge of the soil engineering properties 

 in-situ. It is possible to calculate the in-situ shear strength of a 

 seafloor soil from the results of laboratory shear strength tests on 

 samples. A significant disturbance corrections is usually required 

 since the two strengths may differ by 50 percent or more. The residual 

 negative pore pressure retained by a sample is a good measure of 

 disturbance. 



2. Careful core handling procedures can reduce disturbance and, there- 

 fore, increase the credibility of results obtained. However, most poor 

 handling practices can be compensated for approximately. It also 

 appears possible to compensate for unavoidable forms of disturbance 

 such as pore water expansion. 



3. Gas expansion appears to be one of the most severe forms of 

 disturbance. It may be impossible to estimate the in-situ shear 

 strength through testing of a sample containing a significant amount 

 of gas. 



RECOMMENDATIONS 



1. The procedures of this report are recommended for estimating the 

 in-situ shear strength of a cohesive, near-shore seafloor soil. To 

 apply these procedures it is necessary to obtain a bottom core sample, 

 measure its residual negative pore pressure and vane shear strength, 

 and use the curve of Figure 6 to obtain the in-situ strength. The 

 parameter, u ps (reference residual pore pressure), is required in the 



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