INTRODUCTION 



Obtaining reliable engineering properties of seafloor sediments is 

 a complex and potentially very expensive proposition. The seafloor is 

 remote, the sea is often hostile, and the sediments are unusually soft. 

 Good quality sampling is difficult, and testing in-situ requires expen- 

 sive equipment and considerable ship time. This situation can be im- 

 proved either through the development of more economical in-situ test 

 equipment or through better utilization of soil samples. The latter 

 approach was taken in this report. 



The major problem in engineering property testing of seafloor soil 

 samples in the laboratory has been disturbance. During sampling, 

 transportation, and preparation of specimens, changes occur in the 

 material, causing it to behave differently in the laboratory than it 

 would have behaved in the field. This problem is more severe with sea- 

 floor soils than with land soils because the material is generally 

 softer, the usual types of samplers are more destrictive, and the amount 

 of total stress change during sampling is significantly greater. 



A testing program was formulated to investigate the general prob- 

 lem of sample disturbance with the following specific objectives: 



1. Evaluate the quality of samples taken with the NCEL DOTIPOS 

 bottom-sitting fixed-piston coring equipment (Demars and Taylor, 1971). 



2. Determine how the DOTIPOS core quality compares with that of 

 more conventional gravity cores. 



3. Determine how various forms of disturbance affect the quality 

 of the DOTIPOS cores. 



4. Develop procedures for estimating in-situ strength given re- 

 sults of tests on partially disturbed cores. 



DISTURBANCE MECHANISMS 



A number of possible disturbance mechanisms were identified through 

 a review of the literature. These disturbance mechanisms, with the 

 exception of core shortening and direct temperature effects , were in- 

 vestigated either experimentally or analytically. The results of these 

 investigations are presented in later sections. 



In-Situ Shear Stress Removal 



The in-situ stresses on a soil element are usually anisotropic, in 

 that the horizontal and vertical stresses are not equal. During 

 sampling the element is removed from the ground and then later 



