Rock-fill dikes are composed of various^ more or less regular, 

 layers of stones « The stone depicted in Figure 5 and on -which the action 

 of the wave is exerted in the same manner as on those irtiich surround it, 

 is one of the stones of the first, or exterior, layer of the dikeo The 

 upper face of the second layer is represented by the line E F parallel 

 to the slope o 



If S is the maximum section of the stone in any plane whatsoever 

 parallel to the slope, then the force P, which tends to lift the stone 

 from the slope upon which it rests will be given by: 



in which Kois a coefficient having a value less than unity. This co- 

 efficient introduces correction for the density of the waterj the re- 

 duction in velocity of the liquid molecules in passing through the first 

 layer of stonesj the reduction of the pressure caused by this current 

 meeting the rough and perforated surface of the stones of the second 

 layer in place of the theoretical plane, previously assumed perfectly 

 smooth and continuous | and, last, the reduction of pressure arising 

 from the more or less rounded form of the stone under considerationo 



If for simplification, we make 





we have the expression 



The horizontal component, Vj^, of the maximum velocity V of the liquid 

 molecule of a wave of height A^ breaking in depth A, is as previously 

 determined, /-- — 



The vertical component V^ of the maximum velocity V of the molecules 

 which fall from the height As is 



Then the velocity, V, normal to the plane of the slope will be 

 Substituting this value in the previous expression we obtain 



and setting 



Kz =/^a; 



