Corner spades, 1 5 inches in depth, increased resistance to lateral 

 movements (Figure 27). Sediment in the vicinity of Sea lab II was a dark- 

 gray, micaceous, very fine silty sand with few marine animals and a trace of 

 clay. Analysis of surface cores indicated that the material contained 81% 

 sand, 19% silt and clay. Median diameter of the material was approximately 

 0.004 inch. Laboratory tests of sediment engineering properties gave the 

 following results: angle of internal friction, 22 degrees; vane shear strength, 

 1 .4 psi; buoyant unit weight, 52 pcf. In-situ tests of the seafloor indicated a 

 minimum soil bearing capacity of 1 ,300 psf. A safety factor of three was used 

 to minimize settlement. The seafloor at the site sloped to the southeast at 

 approximately 8 degrees. Typical microrelief was of the order of 4 inches. 

 When Sealab II was positioned, instrumentation showed a 10-degree trim by 

 the stern and a list to the port of 3 degrees. The habitat was then lifted about 

 10 feet from the bottom, rotated, and replaced. A check indicated a port list 

 of 6.54 degrees and a bow-up pitch of 5.96 degrees; these angles did not change 

 appreciably during the three weeks of occupancy. Since Sealab 1 1 was sitting at 

 a lesser slope than the terrain, differential settlement was assumed to have 

 occurred. Measurements on the footings indicated the following settlements: 

 starboard aft, 9 inches; starboard forward, 15.8 inches; port aft, 9.2 inches; 

 port forward, negligible. Later measurements found little additional settle- 

 ment; therefore, settlement apparently occurred on impact or almost 

 immediately thereafter. 



Hydrolab. During October of 1967, Florida Atlantic University 

 placed an underwater research laboratory in approximately 50 feet of water, 

 3,100 feet offshore of Palm Beach, Florida (Stephan, 1969; Perry Oceano- 

 graphies, 1970). The 12-foot-diameter by 20-foot-long habitat, which was 

 designed and fabricated by Perry Oceanographies, was supported on a pre- 

 stressed concrete foundation, 18 feet by 20 feet 8 inches (Figures 28 and 29). 

 Bearing pressure exerted on the coarse calcareous sand bottom was approxi- 

 mately 60 psf. Hydrolab remained in position for 1 1 months. During this 

 period, no movement was detected. Scour and fill were noticeable but not 

 large enough to cause undermining of the Hydrolab foundation. 



This habitat was modified to operate as a one-atmosphere, lock-in/ 

 lock-out facility, and it was placed on the seafloor in 50 feet of water off 

 Riviera Beach, Florida, during July 1969. The soil in the area was a dense 

 sand. The same concrete base, with floodable ballast chambers, was used. 

 In this instance, four 4-foot-diameter metal "cookie-cutter"-type keys 

 extended 1 foot below the concrete base. 



During October 1969, four men spent 2 days living in the Hydrolab 

 during Project Powercel (Ocean Industry, Jan. 1970, p. 23). At the beginning 

 of this project, no scour problems were noted; however, by the end of the 



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