Several different techniques were used to avoid bearing capacity 

 problems when structural loads were large. Typically the organizations 

 involved in design recommended larger bearing surfaces or pile group support. 

 If these measures failed to prevent performance difficulties, the spud-can tech- 

 nique was employed. This procedure consisted of counteracting immediate 

 penetration by installing large-diameter bases to the lower end of cylindrical 

 legs. The large-diameter legs were forced into the sediment as the structure 

 was deployed until sufficient load capabilities were developed to support the 

 structure. 



Problems involving excessive total and differential settlements have 

 been handled in several ways. The petroleum industry found that total settle- 

 ments of mat foundations could be minimized by preloading the foundation. 

 This technique involved subjecting the foundation to excessive loads for an 

 extended period of time. Before actual operations began, the foundation 

 loads were reduced. This concept assumes that all settlements would occur 

 during the period of preloading. Since loads are reduced prior to commenc- 

 ing actual work, any subsequent settlement is thought to be small. 



Differential settlements have been controlled by employing universal 

 joint systems. For example, the hydrophone arrays at the Canadian Range 

 are located between a buoyant sphere and a universal joint. As the structure 

 settles differentially, the sphere rotates the hydrophone about the universal 

 joint back into a vertical orientation. A second technique for reducing differ- 

 ential settlement involves the use of a wide spread on the footing. The larger 

 spread tends to reduce the rotational movements developed by a differen- 

 tially settling structure. Some proposed seafloor structures (MUS, for example) 

 will incorporate level-compensating devices to control differential movements. 



The lateral stability problems encountered by APL in the St. Croix 

 Range were overcome by designing subsequent foundations with keying edges. 

 These structures, which had perimeter cutting edges attached to their bottoms, 

 were dropped from above the seafloor to increase the depth of key penetration. 

 Sealabs 1 1 and 1 1 1 incorporated a similar keying edge on each of the bearing pads. 

 Since ring- or box-type keys (such as those employed at the St. Croix Range) 

 also function as hydrostatic anchors during removal, NCEL engineers have 

 proposed the use of screens or slotted keys for dissipating the immediate 

 breakout forces. 



Several unique designs have been developed for handling environmental 

 problems. Foundations located in shallow water were streamlined to minimize 

 the turbulent motion of bottom currents about the footings. This action 

 reduced, in turn, the degree of undermining by scour. In another case, a pro- 

 tective blanket of coarse-grained material was spread about the foundation. 

 Since bottom currents were not of sufficient magnitude to displace the coarse 



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