When the available equipment and materials suggest a pile anchor 

 system be used to hold the floating breakwater, the required design 

 may be accomplished by one of the methods described below. Anchor piles 

 are designed by finding the ultimate lateral resistance of the pile-soil 

 system and increasing the lateral mooring load, F^, by a safety factor, 

 F Q , to find the design lateral load on the pile, P; i.e., 



F + F 



t r S 



(4) 



The ultimate lateral resistance of the anchor pile is reached when either 

 the passive strength of the surrounding soil is exceeded or when the 

 yielding moment of the pile section is reached. 



Simple design methods, as described in Broms (1964a, 1964b), are 

 divided according to the soil characteristics (cohesionless or cohesive) 

 and by the pile characteristics (short-rigid piles or long-flexible 

 piles) . Only the cohesionless and cohesive short-rigid pile cases are 

 included here because these will normally suffice for anchor piles for 

 floating breakwaters . 



In considering cohesionless soils (i.e., sands), the definition of 

 long versus short piles depends on the calculation of the dimensionless 

 term, x\l , where: 



m 



1/5 



(5) 



and I is the pile length. This term includes the pile section stiffness 

 (EI) and the constant of horizontal subgrade reaction, n^, which is a 

 function of the soil only. Values of n^ are given in the Table; when 

 r\l is less than 2.0 the pile is considered short and rigid and when r\i 

 is greater than 4.0 the pile is long and flexible. 



Table. Values of n^ (from Terzaghi, 1955) 



Embedded soil condition 



Relative density 

 (tons/ft 3 ) 



Loose 



Medium 



Dense 



Above water table 

 Below water table 



7 

 4 



21 

 14 



56 



34 



The short-rigid pile is assumed not to bend when laterally loaded 

 but will rotate about a point approximately 1/3 to 1/4 its length above 

 the pile tip. The soil reaction increases with depth below the firm 

 bottom as shown in Figure 5. 



14 



