The structure is to be placed in a deep ocean basin at a water depth of 

 12,000 feet. The maximum overall slope in the vicinity of the site, as 

 determined from detailed bathymetric charts of the area, is 2 degrees. 

 The microtopography and sediment type were not investigated directly; 

 however, in this geologic province a weak cohesive sediment type and 

 small microtopography would be expected. 



The structure is designed for a deployment of five years. The 

 emplacement capability consists of a 200-foot-long ocean-going Navy 

 tug with a special lowering winch aboard. The load capacity of the 

 boom system is limiting and has a maximum working load of 10,000 pounds. 

 Vertical clearance is 22 feet and outboard reach is 14 feet. Divers 

 will be available to assist with the transfer of the load from the 

 boom system to the synthetic line from the winch. Release of the 

 installation on the seafloor will be accomplished by an acoustically- 

 actuated mechanical release. Recovery of the structure at the end of 

 its deployment will be accomplished by running a heavier recovery line 

 down a guideline which is either released from the structure and rises 

 to the surface or is attached by a submersible. 



Configuration Selection 



This structure, because of its mission, must sit firmly on the 

 seafloor — no rocking can be tolerated. This and the possibility of 

 minor surface irregularity, or microtopography, suggest the use of a 

 multiple, spread footing foundation with articulated individual footings, 

 A life of five years is required; therefore, the use of aluminum and 

 plastic or concrete would be recommended for this case. More exotic 

 materials and coatings could be used, but the initial cost would be 

 much higher. 



Bearing Capacity 



Assume initially that the submerged weight of the foundation will 

 be 500 pounds. 



W , = 4100 pounds 

 sub 



F = 8200 pounds for initial sizing of the footings 



F = 8200 - 3 = 2733 pounds 

 F = 3072 pounds for B = 8.0 feet (Figure 3b) 



Check assumption on weight 

 sub 



W , = 3600 + 3 * (( tt * B 2 * 1/4 * 2) + (4 * B * 6) * 1.5) = 4770 



pounds 



18 



