(4) Design length of a pile anchor. For bottom firm sand 

 (medium relative density), n-, = 14 tons per cubic foot (see the Table) 

 solve for K„ using <)> which .must be known from soil sampling or be 

 estimated (here assume <f> = 30°). 



v - l * sin t - I + °- 5 - 7 n 

 J? ~ 1 - sin <j> = 1 - 0.5 = 3 '° ' 



Select a 16-inch (1.33 foot) steel pipe pile with a 0.1-foot wall 

 thickness . 



E for steel = 2.16 x 10 6 tons/ft 2 



I of cross section = 0.094 ft (from American Institute of 



Steel Construction, 1973) . 



Assume solid bottom is 2.0 feet below anchor line attachment point: 



e = 2 f t . 

 Solving for the characteristic length: 



f^.1 1/5 = / 14 tons/ft 3 \ 1/5 



n LEI J \(2.16 x 10 6 ton/ft 2 ) (9.4 x lO^ft 4 )/ 



n = 0.147 y- . 



Because by definition r\l < 2.0 for the rigid-pile case, try first 

 values of I < 13.6 feet and use the rigid-pile analysis for cohesion- 

 less material to find actual I using equation (6) and rewriting as 



2P I 3 



w s DK p (e + I) • 



Substituting the known values and assuming w = 60 pounds per cubic 

 foot for submerged unit weight of sand: 



I 3 2 x 6,000 lb 



= 50.12 . 



(2 + «,) / lb U1.33 ft) (3) 



♦« (*£)«! 



Then, by substituting for £ as follows: 



Assume Calculate Compare to 



£(ft) l 3 /{2 * gQ required value 



7 38.111 < 50.12 



8 51.20 > 50.12 by small amount 



9 66.27 > 50.12 



19 



