3l6« The couple (F) due to the two pressure dia£;rams is applied at 

 the centroida of the tvjo triangles, and the moment due to this couple 

 must equal the overturning moment about the neutral axis. Therefore the 

 overturning forces may be represented by 



F = 3M (83) 



lb 



For stability these forces should at least equal the resisting forces due 

 to the crosswaH^ls and fillj so 



F = 3M - S « P (^rf + tan 0) (g^) 



2b L 



The minimum width of the equivalent rectangular cell section for stability 

 is 



V 3M - 



2 P (£| . tan 0) ' (85) 



where 



M a the total overturning moment about the center line 



P s the total force due to the cell fill 



r s the radius of the outside cell wall 



f s the coefficient of interlock friction 



L s cell section length 



tan 3 the coefficient of internal friction of the cell fill, 



31 7. Overtui'ning SeavJard . - The maximvim overturning moment due to 

 the backfill will be caused by a saturated backfill with no water in 

 front of the wallo From the section on earth forces, this backfill 

 force would be Bs3hO pounds per lineal foot of wall applied at a distance 

 I1.I1.8 feet above the base_, giving a moment of 23^900 foot-pounds per 

 lineal foot of wall. Assuming an interlock friction coefficient of 0.3, 

 an unsaturated cell fill, and a cell length of i;0 feet, the equation 



for minimum width would become 



b s ^^3^900__„, . « 15.1 feet, say I6 feet 



2 X 1730 ( 50 ^^Q°3 ^ ^) 



the maximum width between outside walls would be b^ = b/O.9 s 17.8 feet, 

 say 18 feet. 



318. Ov erturning Landward . - Similarly the maximum overturning 

 moment due to Xirave forces will be that due to the maximum wave impinging 



