Figure 35 compares the total carbon content with the original 

 strength of the soil. The total carbon content include both the carbonate 

 carbon and organic carbon contents. If the soil derived a significant 

 portion of its strength form the carbon content, a relationship between 

 shear strength and carbon content would be expected. However, these data 

 fail to indicate such a relationship. It seems that for these soils 

 carbon content plays an insignificant role in the development of strength. 



SUMMARY AND CONCLUSIONS 



Strengths and index properties were determined from soil samples 

 taken at 18 locations in the southwest Pacific and eastern Indian Oceans. 

 These data can be used to provide a preliminary indication of the seafloor 

 soil conditions that exist in those ocean areas. 



It is believed that the data presented for abyssal hill and abyssal 

 plain provinces are sufficiently reliable to provide relative comparisons 

 of soil conditions at different sites. Discrepancies between the test 

 data and in-situ conditions that may be attributable to inadequate coring 

 procedures, poor sample handling, or improper testing have been discussed. 

 Since these discrepancies would typically lead to indications of soil 

 strengths lower than those existing in situ, a foundation design based 

 upon calculations using these data would be on the conservative side. 

 However, the utilization of these data should be restricted to nonessen- 

 tial or expendable facilities. 



With the test sites divided into three physiographic provinces, 

 namely continental terrace, abyssal plain, and abyssal hill, a significant 

 amount of data scatter was found to exist between similar provinces. 

 Before it will be possible to develop regional charts of soil properties, 

 more precise definitions of the boundaries of physiographic provinces will 

 be required. 



The shear strength and index properties of abyssal hill and abyssal 

 plain sediments differ. The nature of the difference may depend upon the 

 mineral constituents of the material; the dependency appears to be masked 

 by time -dependent phenomena. Sediment strengths in the upper 150 to 300 

 centimeters showed little relationship to index properties. Consequently, 

 a disturbed sample cannot presently serve as an index of the sediment 

 strength. 



RECOMMENDATIONS 



The results of the investigation suggest several areas for additional 

 research: 



1. Correlate the effect of high area ratio of corers on strength 

 loss. In particular, determine the strength loss at the center of a 

 gravity core. 



2. Investigate the mechanism of soil strength in the upper 150 to 

 300 centimeters of soil. 



37 



