in which a foundation is selected and sized and then checked for adequacy. 

 If it falls short in any regard, it is modified and checked again until 

 a satisfactory design results. 



The input information on the structure includes the structure's 

 dry and submerged weights (W sc j and W sw ) , its maximum dimensions C^^, 

 y max , z max ) and its maximum lateral projected area (A^) . These values 

 will, of course, be different from those for the final installation 

 which will include the foundation. 



Knowledge of the sites for structures in this category usually 

 consists only of the geographic location, the water depth, and the 

 geologic province — including general slope. Information describing 

 the geologic province (examples of geologic provinces include deep 

 ocean basin, seamount top, and continental shelf) should indicate 

 whether rock or sediment will be encountered on the seafloor. This 

 determination has a large effect upon the foundation design. However, 

 if it cannot be made, the foundation should be designed for sediment. 

 Such a foundation will usually suffice for a rock bottom whereas the 

 reverse situation would not be satisfactory. Knowledge of the general 

 slope of the site, such as from bathymetric charts or surveys, is needed 

 for calculations concerning overturning. Foundations in this category 

 should not be located on slopes steeper than 10 degrees. Foundations 

 for such slopes are possible; however, they require more detailed site 

 investigations and analyses, which are beyond the scope of this report. 



The expected emplacement capability influences the foundation 

 design process primarily by limiting the spread of the foundation 

 elements. Larger spread is desirable to increase stability against 

 overturning; however, this generally increases the minimum lateral 

 clearance radius (r^) , the vertical projected area (A ), and the 

 installation's weights (Wi and Wg^) , all of which may be limited by 

 the available emplacement capability (ship, boom length, line working 

 load, and winch capacity) . 



A foundation consisting of three articulated spread footings 

 (similar to Figure la) is often the most desirable configuration, although 

 not the least expensive. Either circular or square individual spread 

 footings can be used. If the seafloor is expected to be relatively 

 smooth (small microtopography and surface roughness) then a ring footing 

 (similar to Figure 2b) or two strip footings (Figure 2h) would be 

 equally satisfactory and simpler to fabricate. A single spread footing 

 is usually less desirable because it offers less resistance to over- 

 turning in comparison to other types. However, it can often be the best 

 selection from both deployment and ease of fabrication standpoints. 



In designing the actual configuration it is desirable to locate 

 the structure as low on the foundation as practical and to center it 

 relative to the foundation element or elements, as nearly as possible 

 with respect to submerged weight, mass, and resultant force from 

 current drag. These three are most often not at the same point. In 

 fact, it is typically difficult to determine these three precisely; 

 however, an awareness of this consideration during the early design 



