The pressure distribution is shown by DC in Figure 97. 



288, Bearing Piling . - Since the maximum base pref5sure exceeds the 

 allowable bearing capacity of the foundation material, piles must be used 

 to support the wall. The design piling load along a section of wall 



may be calculated by uniformly subtracting the bearing icapacity of the 

 foundation material from the total foundation pressure/ The remaining 

 foundation pressures must be supported by piles. In this case, subtract- 

 ing the bearing capacity of the soil as shown by the line EF on Figure 

 97, piling would be required to support the load DEG, which is 



^DEG = -|- X 3900 X EG 



EG being given by -^ = sffo' ^ ^ ^'^ 



Therefore F s 17,700 pounds per foot applied at a distance l/3 EG s 3.03 

 feet from A, 



289, Allowable pile loadinp vrries with the jnateria]. in which the 

 pile is driven. If i\n individual pile rests on a hard stratum its bear- 

 ing capacity is determined by the ultimate strength in compression cf 

 the pile material. Essentially the pile becomes a totally laterally 

 supported column. However, when a pile's bearing load is supported 

 primarily by skin friction with the material through which it is driven, 

 its bearing capacity must be determined by empirical means, 



290, For most foundation materials on which seawalls vxill be built, 

 the resistance to a static load is almost the same as that offered to 

 the dynamic load of driving. The allowable bearing load per pile can 

 thus be calculated by relating the depth of penetration of a test pile 

 per blow to the hammer weight. Relationships comiaonly in use for- timlaer 

 and concrete piling are as follows: 



TABLE 27 - Safe Load i^ef I'ile 



Driver Timber Concret e 



n u . 2Wh ^ 2Wh 



iJrop Hanuiier F = r — r~t i = ~—r^~~rT: — T^T'' 



^ b + 1 s (1 + VVp/W 



Steam hammer, sinple acting P = ^^^'^ ■■ , P == 2^1^..__ 



s + 0,1 s -1 0.1 Wp/VJ 



Steam hamiaer, double acting P = 2h (W * ap) p _ 2_(W_J_a£) _ 



s + 0.1 s + 0.1 Wp/W 



II42 



