For sites in the vicinity of seamounts , rises, hills, trenches, and 

 similar seafloor features of large relief, generalizations concerning 

 slopes can be dangerously misleading from a foundation design standpoint. 

 The actual slope must be determined for each such individual site, and 

 in many cases will be too steep for foundations described in this 

 report. 



In this design process the worst case is assumed: the effective 

 lateral force resulting from the inclination of the foundation is 

 assumed to act in the same direction as the drag force resulting from 

 currents and surge. In order for the foundation to resist these lateral 

 forces and to prevent the possibility of the installation skidding down 

 the slope as a result, it is necessary that the installation, with or 

 without keys, satisfy the following inequality 



F. + F, < 0.5 * W , (4) 



1 d — sub 



If this is not the case, then the design should be changed (weight 

 can be added or the area, Ai, reduced). Once inequality (4) is 

 satisfied, it may still be necessary to consider the use of keys (see 

 Figure lb) on the base of the foundation. In general, it can be assumed 

 that a properly proportioned foundation with no keys has an effective 

 coefficient of friction of 0.1 with the soil. Thus, its lateral 

 resistance, F , is given by the equation: 



F, (pounds) = 0.1 * W , (pounds) (5) 



n sub 



If the bottom material is known to be clean sand or rock, a value of 

 0.3, rather than 0.1, may be used for the coefficient. If the sum of 

 F^ and Fj is greater than F^ then keys must be used. For the general 

 case (presumed not to be on rock or clean sand) perimeter keys should 

 be made of material between 0.2 and 0.4 inches in thickness. Their 

 required depth, d , is given by the equation: 



d (feet) = 0.17 + 0.05 * B (feet) (6) 



When keys are used, the footing should have holes or other provisions 

 to allow the water entrapped by the keying edge during emplacement to 

 escape. If it is known that the footing will be placed on clean sand 

 and that keys are required, the key depth, d e , should be reduced to 1/3 

 the value calculated from Equation 6. On rock a number of pointed 

 bars 1/2-inch in diameter extending 3 to 6 inches below the footing, 

 spaced every 6 inches to 1 foot around its perimeter, and pointing 

 slightly outward (15 to 30 degrees relative to vertical) make an 

 effective design. 



