> 



3 Wp 



(a) deflections (b)soil reactions 



mox 



(c) BENDING MOMENT 



Figure 5. Failure modes for a short-rigid pile in 

 cohesionless soil (after Broms, 1964b). 



Because anchor piles are designed for the soil's ultimate lateral 

 resistance rather than deflection of the pile head as in structural piles, 

 the design is predicated on sufficiently large deflection to develop the 

 full passive resistance. This is defined, based on comparison with test 

 data, as three times the Rankine passive Earth pressure from the ground 

 surface to the center of rotation (Broms, 1964b). The resulting equation 

 for ultimate lateral resistance is: 



w D £ 3 K n 

 s P 



2(e + I) 



(6) 



where 

 P 

 D 



s 

 e and £ 



b 



= design lateral load (P = F^Fg,, eq. 4) 



= characteristic width of pile (the diameter for pipe pile) 

 = unit weight of soil 

 defined in Figure 5 

 = Rankine's coefficient of passive Earth pressure; 



1 + sin d> 



K P " j 



sin 4> 



<f> = angle of internal friction of sand 

 Equation (6) may be solved by iteration as shown in the example, 



(7) 



