The Naval Research Laboratory also has placed submerged test units 

 at two shallow-water sites. During 1961 , a cagelike structure was recovered 

 monthly from a water depth of 300 feet near Fort Lauderdale, Florida. The 

 array, which had a 3- by 4-foot concrete base weighing 200 to 300 pounds, 

 was placed on a calcareous sand bottom. No sinking was ever noted. Another 

 unit was deployed near Fort Lauderdale in 500 feet of water for 12 months. 

 Sediments at the site were calcareous oozes. The unit, which used a deacti- 

 vated mine for a base, weighed approximately 1 ,000 pounds. No settlement 

 was noted when observed with television camera just prior to recovery. 



NUSL Transponder Block. A small transponder block was placed in 

 the Long Island Sound near New London, Connecticut, by the Naval Under- 

 water Sound Laboratory (NUSL). The water depth at the site was approximately 

 60 feet, while sediments in the area were predominantly sands. Divers observed 

 that the 3- by 3- by 1 -foot concrete block base and the acoustic relay cables 

 have been partially covered with sand (Moothart, 1969). 



NUC Pop-Up Test Site. Two foundation types have been used by the 

 Naval Undersea Research and Development Center (NUC), Pasadena (formerly 

 Naval Ordnance Test Station), for pop-up tests conducted off the northwest 

 tip of San Clemente Island (Gardner et al., 1969; Sutton, 1969; Ridlon, 1969). 

 The first foundation was installed in 1958 to test Polaris-type missiles. The 

 foundation, which was in 1 1 5 feet of water, employed a 30-foot-diameter by 

 9-foot-high concrete-filled steel caisson. This caisson was embedded 7 feet 

 into the soil. The soil profile consisted of 8 feet of loose coarse sand atop a 

 6-foot layer of dense sand. A fractured andesite with pockets of gravel lay 

 beneath the sand. This foundation supported a 400,000-pound launcher; 

 additional dynamic compression loadings as large as 1 40,000 pounds resulted 

 during individual tests. No foundation problems were reported. 



In 1960, a more complex launch system (Figure 20) was installed in 

 170 feet of water at a nearby site. The soil profile was essentially the same. 

 This system had a static weight of over 700,000 pounds and resisted dynamic 

 compression loads of up to 220,000 pounds during individual tests. The test 

 structure was supported on four 14-inch-diameter by 65-foot-long drilled-in, 

 grout-filled, pipe piles. Over 200 simulated launchings have been performed. 

 Although no foundation monitoring was provided, it is known that the thresh- 

 old sensitivity of other electronic equipment mounted on the structure 

 (differential movement of less than 1/8 inch) was not exceeded. 



Two camera mounting piles, which extend to the ocean surface, have 

 also been installed at the Pop-Up Test Site. These 24-inch-diameter piles were 

 drilled in 36 feet and filled with grout. The piles were designed primarily to 

 resist a maximum overturning moment of 410,000 ft-lb caused by wind and 

 wave forces. The two structures have exhibited no serious foundations pro- 

 blems. 



34 



