, ,_ /w -w \l/2 / . 2^\l/4 , ,- 

 V = 1.20 (2g)l/2 l~^) 1- ^1 d/2 (7_1,1) 



\ W / y sin ^1 ^ 



This is Isbash's equation for stone embedded in the bottom of a sloped channel 

 modified for stone embedded in a bank with angle 6 to the horizontal (the 

 coefficient 1.20 is Isbash's constant for embedded stone). From this, the 

 armor stone weight required to withstand the velocity V is as follows: 



W = 



„6 w -w , 



V r W 



(1.20) (2g) (w^-w^l L _ sin 9 ^ 



• 2^ 

 sin (j) 



W = 0.0219 -^T-^ ^^ 1-^^^^ (7-142) 



V. IMPACT FORCES 



Impact forces are an important design consideration for shore structures 

 because of the increased use of thin flood walls and gated structures as part 

 of hurricane protection barriers. High winds of a hurricane propelling small 

 pleasure craft, barges, and floating debris can cause great impact forces on a 

 structure. Large floating ice masses also cause large horizontal impact 

 forces. If site and functional condition require the inclusion of impact 

 forces in the design, other measures should be taken: either the depth of 

 water against the face of the structure should be limited by providing a 

 rubble-mound absorber against the face of the wall, or floating masses should 

 be grounded by building a partially submerged structure seaward of the shore 

 structure that will eliminate the potential hazard and need for impact design 

 consideration. 



In many areas impact hazards may not occur, but where the potential exists 

 (as for harbor structures), impact forcer should be evaluated from impulse- 

 momentum considerations. 



VI. ICE FORCES 



Ice forms are classified by terms that indicate manner of formation or 

 effects produced. Usual classifications include sheet ice, shale, slush, 

 frazil ice, anchor ice, and agglomerate ice (Striegl, 1952; Zumberg and 

 Wilson, 1953; Peyton, 1968). 



There are many ways ice can affect marine structures. In Alaska and along 

 the Great Lakes, great care must be exercised in predicting the different ways 

 in which ice can exert forces on structures and restrict operations. Most 

 situations in which ice affects marine structures are outlined in Table 7-14. 



7-253 



