and combining Equations 7-23 and 7-27 gives 



F^ = F^)^ cos0|cos0|, 

 where 



_ 27rx 27rt 

 ~ L T ■ 



The wavelength can be found from Figure 7-40, 



L « L^ = 554 ft. 



From Table 7-4 or Figure 7-60 the maximum force on the example pile 

 occurs when 20° < 8 < 40°, and is about F^ « 25,000 lbs. 



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EXAMPLE PROBLEM 



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GIVEN : Two piles each with a diameter, D = 4 ft., spaced 100 ft. apart 

 are acted on by a design wave having a height, H = 35 ft., a period, 

 T = 12 sec. in a depth, d = 85 ft. The direction of wave approach 

 makes an angle of 30° with a line joining the pile centers. 



FIND 



The maximum horizontal force experienced by the pile group and 



the location of the reference pile with respect to the wave crest 

 (phase angle) when the maximum force occurs. 



SOLUTION : The variation of total force on a single pile with phase 

 angle 6 was computed from Airy theory for the preceding problem 

 and is given in Figure 7-60 and Table 7-4. Figure 7-60 will be used 



7-117 



