76 THE NAVY OCEAN ENGINEERING PROGRAM 



SEA FLOOR ENGINEERING 



The ability to design and construct facilities for the ocean bottom re- 

 quires developments in sea floor engineering. Problems include site selec- 

 tion and survey, structural analysis of fixed structures, fabrication and 

 assembly of components, bearing capacity of bottom sediments, and the 

 design and placement of anchors, and foundations on the ocean floor. 



The data on soil properties will be applied to the engineering design of 

 foundations for underwater installations. Primary concern in foundation 

 design and construction will be with safe bearing capacity based on toler- 

 able settlement, rather than on the ultimate bearing capacity, which is the 

 bearing stress necessary to rupture the soil mass beneath footing. Bottom 

 soil properties are being studied to define their engineering characteristics. 

 Sediment cores are taken from the bottom of the sea to determine the sig- 

 nificant parameters of the soil which will affect the design of a sea floor 

 installation. Core samples retrieved by the Navy Civil Engineering Labo- 

 ratory from various depths in the ocean have indicated varying mechanical 

 properties. 



Laboratory test data alone will not be sufficient to determine the 

 ocean floor bearing capacity. Environmental investigations to determine 

 soil properties are required, and methods to accomplish this are being 

 developed. 



One device which will aid in determining the engineering properties of 

 marine soils is the in situ plate bearing device. This device is capable of 

 determining the short-term bearing pressure and settlement response of 

 marine sediments as it operates on the sea floor while connected to a 

 surface vessel only by a load-bearing line. Tests with this plate bearing de- 

 vice have been performed on both cohesive and noncohesive soils in depths 

 to 1 200 ft. It was found that the size of the bearing plate was the most 

 significant parameter affecting the bearing pressure and settlement re- 

 sponse in both major sediment types. 



A second tool being developed for engineering investigations is the 

 in situ vane-shear device. This device will be capable of performing vane- 

 shear tests to a depth of 10 ft below the sea floor in a maximum depth of 

 6000 ft of water. Research will be performed (a) to obtain in place meas- 

 urements of soil strength properties, (b) to relate in place data to labora- 

 tory tests of cores taken from the test sites, and (c) to determine the rela- 

 tionships between environmental vane-shear measurements and the more 

 rapidly obtained core-penetrometer measurements for the various sedi- 

 ment types. 



