particles, scour was controlled. A third technique for controlling scour 

 involved perimeter curtains around the foundations. These curtains extended 

 the depth of scour necessary for causing structural undermining. The latter 

 two techniques also could be effectively used to prevent undermining by 

 marine animals. 



The other environmental problem which necessitated unique 

 foundation designs involved the irregular topography of the seaf loor. Pro- 

 posed habitats (MUS) will incorporate adjustable, articulated legs for leveling 

 the structure on uneven slopes and maintaining bearing contact. The Tektite 

 and Sealab I projects avoided some problems associated with irregular topo- 

 graphy by physically leveling the sites. A screed-type apparatus removed the 

 high points and filled in the low points before the habitats were placed. 



Deployment problems were generally related to the handling of the 

 structure at the surface and the correct positioning of the structure on the bot- 

 tom. Handling problems have been reduced by equipping the various habitats 

 with buoyancy tanks. These tanks permitted the habitats to be floated to the 

 site. By flooding the tanks, negative buoyancy was achieved, and the habitats 

 sank to the bottom. Positioning problems have been reduced by employing 

 either cable or pile guides. The rate of descent was controlled during deploy- 

 ment by hanging weights beneath the structure (Makai Habitat). Once the 

 weights came in contact with the bottom, the net negative buoyancy was 

 decreased. The rate of descent was thereby reduced to a more controllable 

 level. 



SUMMARY AND CONCLUSIONS 



This report describes a number of seafloor installations with respect 

 to basic foundation design parameters and foundation performance. These 

 installations include offshore towers, manned habitats, acoustic arrays, and 

 various research test units. All of these seafloor structures, or installations, 

 require some form of foundation through which vertical and horizontal forces 

 are transmitted to, and resisted by, the seafloor. 



Performance problems have been encountered by a number of these 

 foundations, and failures have occurred in a few cases. Of the approximately 

 400 installations for which information was found to be available, 4% experi- 

 enced performance problems and an additional 3% failed. Numerous other 

 seafloor foundations performed satisfactorily, but the factors of safety incor- 

 porated in their design were very high so that the cost of fabrication and 

 deployment may have been excessive. 



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