Recovery 



Since this installation will presumably be located on a cohesive 

 sediment, large breakout forces can be expected during recovery. The 

 total force required at the seafloor during recovery could easily be 

 of the order of 15,000 pounds. One means of reducing this would be 

 to use breakaway footings . 



Design Example Two 



The second example design problem is a small structure to be 

 deployed at a water depth of 70 feet in a bay near the entrance. The 

 structure is an environmental monitoring and recording instrument which 

 is to be deployed for 3 months to collect data on bottom current 

 velocity and direction, tide, water temperature, and salinity. The 

 information is to be used eventually in the design of a large permanent 

 mooring. The instrument is quite small; however, it is necessary to 

 "design" the foundation for two reasons. First, the economic cost of a 

 foundation failure would be quite high in terms of expended effort and 

 lost data. Second, as will be seen, the required foundation is often 

 quite different from what one might expect. The use of a "typical sized 

 foundation" for this case would likely lead to a foundation failure. 



The maximum slope of the site as determined from bathymetric 

 charts is 6 degrees. Diver observations of the bottom at the site 

 indicate very small microtopography and a clean sand bottom. The latter 

 observation was confirmed by samples. The available emplacement and 

 recovery capability consists of a crane barge which can handle up to 

 10 tons directly to the bottom. Vertical clearance going over the side 

 is 30 feet and clear outboard reach is 22 feet. Divers can work off 

 this barge and will be available for both emplacement and recovery. 



The structure consists simply of a vertical cylindrical case, the 

 lower 18 inches of which is an open frame containing various sensors. 

 The characteristics of the structure are as follows: 



x = y =1 foot 

 max max 



z =6.83 feet 

 max 



A.. = 6.83 square feet 



W , = 350 pounds 

 sd 



W = 135 pounds 

 sw 



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