or by the marine organisms that always seem to be attracted to installa- 

 tions deployed on the seafloor. Figure 2f is a later version of the 

 same footing design. This version has a reduced effective footing edge 

 thickness, t , because the outer structural angle has been eliminated 

 (by using heavier members elsewhere) . These spread footings are designed 

 with plastic (PVC) in contact with the soil where corrosion rates are 

 high and with welded aluminum, oversized to allow for corrosion, as 

 the structural backing. 



Figure 2g is a large spread footing (B = 14 feet) made of heavily 

 reinforced concrete. A welded steel keying edge (with d e = 10 inches) 

 surrounds the perimeter. The horizontal edges of this footing are 

 contoured in an attempt to streamline the footing to bottom currents 

 and thus to lessen the chance of scour and undermining. Concrete 

 was used in this case to provide additional weight to properly embed 

 the keying edge. 



Figure 2h illustrates a structure supported on two strip footings 

 (each having B = 2 feet and L = 12 feet) made of aluminum. This 

 structure is designed for recovery from deep water after deployment for 

 up to several years. The footings are therefore attached with magnesium 

 bolts , which are designed to corrode away rather rapidly upon exposure 

 to the sea water so that the footings are not attached at the time of 

 recovery, thus avoiding the problem of breakout associated with all 

 soils except clean sands, gravels, and rock. 



The last illustration on Figure 2 shows a multiple stubby pile 

 foundation designed for a rock bottom. A small footing is built into, 

 but located just above, the point of each pile. This is in case the 

 rock is weak or covered by sand and the pile would have a tendency to 

 penetrate. In either of these situations, these plates would act as 

 small spread footings and prevent excessive penetration. Under normal 

 circumstances, three such piles would be desirable to ensure equal 

 loading of each, and thus prevent rocking of the foundation. 



The nine foundations illustrated in Figure 2 are representative 

 of the types of configurations now in use for seafloor foundations. A 

 few of the nine illustrated are designed to support larger and heavier 

 installations. Thus, some are larger or slightly more complex than 

 may be required for the smaller of the installations being covered by 

 this report. The design considerations would, however, be basically 

 the same. 



DESIGN 



Design Conditions 



The foundation design process starts with inputs from three areas: 

 (a) data on the structure to be supported; (b) information describing 

 the site; and (c) information on the limitations of the planned emplace- 

 ment technique. The design process itself is basically an iterative 

 process, or in many applications simply a trial and error procedure, 



