deep water either syntactic foam or glass spheres can be used. The 

 latter are usually less expensive; however, if several are required in 

 close proximity, there is the possibility of sympathetic implosion of 

 all if one should implode. In water depths less than about 1000 feet, 

 buoyancy tanks (larger pressure-resistant structures filled with air) 

 and less expensive foams are practical. In general, however, reduction 

 of total submerged weight is not as practical as redesigning a founda- 

 tion to handle the load. The addition of buoyancy increases the volume 

 of the structure and, therefore, the lateral loads. It also increases 

 the dry weight and mass of the structure. This generally increases 

 the difficulty of handling and emplacement. 



A third consideration concerns installations which are just 

 slightly negatively buoyant. Installations should not be designed with 

 an effective total density approaching that of seawater because sediment 

 in suspension in the seawater can increase its effective unit weight. 

 The maximum effective fluid densities possible in a sediment cloud are 

 not known; however, during routine laboratory soils experiments, 

 increases of 6 percent are regularly created and can endure for hours 

 with no outside agitation. Such an increase in fluid density would 

 have a tremendous influence on the submerged weight of an installation 

 which was nearly neutrally buoyant in clear seawater. In some extreme 

 cases it would be possible that an installation, which was just slightly 

 negatively buoyant in clear seawater, would be simply floated off in 

 such a sediment cloud. 



Foundation Emplacement Considerations 



This section is included for two reasons. First, a significant 

 percentage of foundation performance problems are caused by improper 

 emplacement, and second, foundation design is often seriously restricted 

 by considerations of available handling and emplacement methods. These 

 considerations, their effects upon the foundation design, and other 

 considerations in foundation emplacement are discussed in the general 

 order of their occurrence in an actual emplacement operation. 



The installation, foundation and structure together, must be designed 

 with a lifting point, or points for a sling, which will provide the 

 proper orientation of the installation in water. An installation will 

 often not have precisely the proper orientation when suspended by this 

 point, or points, in air. This is satisfactory as long as it is stable 

 in air. This lifting point should be well above the center of gravity 

 of the installation, both in air and in water. A number of points 

 should be provided for attaching securing lines during shipment and for 

 tag lines during handling over-the-side. The foundation must rest on 

 the deck of a ship before it rests on the seafloor. This often 

 necessitates the use of special blocking or a second support system since 

 installations are often much heavier in air. 



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