because the surface strength of the soil was insufficient to resist the lateral 

 component of the structure's weight. The sliding problem was not anticipated, 

 since slopes were between 1 and 1 5 degrees. Now that a foundation failure 

 of this type has occurred and there is general awareness of this problem, spe- 

 cial footing configurations have been fabricated to minimize the possibility of 

 future occurrences. However, an analytical technique for designing such fea- 

 tures has not been established. Foundation breakout has proven to be a problem 

 of concern in at least one case. Conshelf Three personnel experienced anxious 

 moments on the bottom when the habitat refused to break free after ballast 

 was released. Several of these areas (breakout, anchor capacity) are currently 

 being investigated. Once a reliable analytical technique for predicting perfor- 

 mance is developed, it will be essential to verify the technique with field 

 experience. 



The second major cause of foundation problems involves the effects 

 of various environmental factors. Many of the problems are associated with 

 wave forces; however, other factors such as marine life and topography have 

 influenced the integrity of certain systems. In shallow-water areas (less than 

 400 feet), the seafloor surge resulting from surface waves has caused exten- 

 sive scour and fill about some footings. Up to 50% of the area beneath some 

 LOBSTER footings and about 25% of the area beneath the Hydrolab were 

 undermined. In the case of the LOBSTER footings, large differential settle- 

 ments followed as the footing tipped into the scour pit. Fill caused by current 

 action has, in turn, deposited several inches of material over the NUSL trans- 

 ponder block. The same wave forces have disrupted the normal arrangement 

 of cables for acoustic arrays at the BARSTUR range. Surface waves also 

 affected the performance of one and possibly two other structures. Four 

 piles driven through the corners of a floating barge into the sediment at the 

 Tektite site failed in fatigue after being subjected to the oscillatory motion 

 of a barge floating in the water. In another instance, a mooring line attached 

 between a surface ship and the Hydrolab may have permitted the motion of 

 the ship to transmit an oscillatory force to the habitat. The resultant force 

 variation could result in a partial liquefaction of the sandy material beneath 

 the foundation. 



In deep water, the seafloor surge action caused by surface waves 

 decreases; however, a more uniform current may still affect the integrity of 

 the structure. In addition to causing scour or fill about an object, the currents 

 may impart significant lateral loads to the side of the structure. At the Cana- 

 dian Range, the lateral loads, in turn, caused excessive differential movements 

 of the structure. 



Another rather unusual parameter which led to the unsatisfactory 

 performance of a foundation was the undermining action by marine life. 

 Animals which burrowed beneath a few of the LOBSTER footings caused 



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