The three most important considerations in selecting a foundation 

 configuration in this case are the large current drag forces at this 

 location, the lack of significant micro-relief, and the relatively 

 short duration of the deployment. The least expensive type of founda- 

 tion would be a single spread footing, but it is not as efficient in 

 resisting the expected large overturning moments as is a crossed strip 

 footing. The latter is almost as inexpensive to fabricate and since 

 there are insignificant limitations imposed by the available emplacement 

 capability, the crossed footing configuration will be tried. Since 

 the deployment is for a relatively short period of time and additional 

 weight in the foundation will be useful in resisting the effects of 

 the current drag force, standard structural steel will be selected 

 for the material. 



Bearing Capacity 



Assume initially a foundation with a submerged weight of 500 pounds. 



W , = 135 + 500 = 635 pounds 

 sub 



Doubling this load to initially size the footings, 



F = 1270 pounds 



Try B = 1.5 feet, 



F = 24 pounds per foot, or for clean sand 48 pounds per foot 

 (Figure 3a) 



2*L-B=F*F..=26.5 feet 

 all 



L = 14 feet 



Checking the assumed foundation weight, the submerged weight of steel 



plate 1.5 feet wide by 5/16 inch thick with two 1-inch stiff ners is 

 18.5 pounds per foot. 

 Total weight would equal, 



F = (2 * L - B) * 18.5 = 490 pounds, which is satisfactory. 



Lateral Forces 



Drag force due to bottom current, 



F = 60 * A, (2) 

 d 1 



22 



