substantial differential settlements. Results of another experiment at the 

 same site (Muraoka, 1 970) suggested that U-shaped wormholes in the area 

 may have contributed to excessive footing settlements. 



Rough topography has also caused unsatisfactory performance of 

 several seaf loor foundations. Rock terrain near the Conshelf Two site pre- 

 vented use of the conventional bearing pad foundation. The large slope at 

 the Sealab II site was the cause of the habitat tilting. 



The last major area of consideration involves deployment techniques. 

 The number of foundation difficulties associated with this parameter seems 

 to vary with structural size and depth of deployment. Small structures such 

 as the SCAR F hydrophone arrays have apparently been tipped over during 

 the installation phase. Another problem often associated with the deploy- 

 ment technique involves the final location of the device. In several situations, 

 the final position of the object was substantially removed from the area of the 

 soi I's investigation. Properties and surface consistencies varied between the two 

 locations. 



Unique Foundation Features 



These performance problems generated several new approaches 

 to design and deployment. Of greatest apparent benefit has been the reali- 

 zation that performance problems do occur and that, if performance is to be 

 satisfactory, some form of analysis should be performed before deployment. 

 More accurate site surveys, which include better soil analysis, and updating 

 of analytical techniques have been two other more immediate results. Several 

 unique foundation designs for combatting the more unusual performance pro- 

 blems also evolved. In some cases these unique designs were based upon the 

 results of analytical calculations. However, in most cases an empirical approach 

 to design was employed. Regardless of their origin, these unique designs, sum- 

 marized in the following paragraphs, have increased the performance reliability 

 of some seaf loor structures. The design engineer should, therefore, consider 

 incorporating some of these preventive actions if soil, environmental, or 

 deployment difficulties are anticipated. 



The bearing capacity problems associated with the low-strength, 

 cohesive materials of river deltas and deep-sea areas have been avoided by 

 decreasing the net bearing pressure on the soil. Various buoyant objects such 

 as syntactic foam modules or buoyancy chambers have been attached to the 

 structure to decrease the total unit weight. This approach is typically employed 

 on smaller, lightweight structures since the amount of buoyancy achieved varies 

 directly with the amount of fluid displaced and the module's weight. Two typi- 

 cal seaf loor systems employing this buoyancy concept are the Canadian and 

 St. Croix hydrophone arrays and the manned habitats (Sealabs, Conshelfs). 



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