The groin spacing within the zone of shortening should decrease to maintain 

 the design ratio between spacing and length. Since the lengths of the groins 

 in this zone differ, the spaae-to-length ratio, r , , is based on the 

 average length of adjacent groins. By maintaining this ratio, the spacings 

 shown in the figure are 



(5-9) 



(5-10) 



and 



(5-11) 



Since the length of transitional groins and their spacings are interdependent, 

 the equations for lengths and spacing are combined as follows: 



1 r— tan 6 



., =|— ^^;^ K (5-12) 



, 1 + -|i tan 6" 



and 



s, = 



si 



1 ' \l 



(5-13) 



1 + -=-=■ tan 6 



*************** EXAMPLE PROBLEM 3*************** 



The example computation is based on the shortening of the three groins 

 shown in Figure 5-19. If the normal spacing of a groin field, s^^ , is 152 

 meters (500 feet) and the normal groin length, i , is 76 meters (250 feet) 



R = — Q^ - 152 = o n 

 ^sl £jj " 76 ^'^ 



then using equation (5-12) 



5-47 



