When actually computing forces on sheet-pile groins and jetties, the re- 

 storing force caused by water and wave action in the structure's leeward 

 side must also be considered. The critical design situation occurs when the 

 water surface on the leeward side is a minimum; i.e., when a wave trough 

 acts there. For the example, the worst case for overturning moment exists 

 when the water level on the leeward side is equal to y^^ = 8.83 feet. This 

 corresponds to a minimum restoring force of 2,400 pounds per foot. 



A critical factor not included in the example that must be considered in 

 any real design problem is the force arising because of the differential 

 sand elevation on each side of the structure. These forces must be based on 

 estimates of the maximum deposition and scour that will be experienced dur- 

 ing the lifetime of the structure. It is also possible that this critical 

 condition will occur during construction unless a scour blanket is placed 

 adjacent to the structure. 



VI. SUMMARY 



The proposed method for computing the distribution of wave force and 

 overturning moment along a vertical sheet-pile groin or jetty is approxi- 

 mate. It assumes that the force and moment are in proportion to the nonlinear 

 wave profile as given by the cnoidal wave theory. Alternatively, any other 

 appropriate wave theory to describe the profile could be used. The assumption 

 that a wave crest or trough acts uniformly along structures oriented nearly 

 perpendicular to shore grossly overpredicts the total force since only a small 

 part of the structure is acted on by a wave crest at any instant. The use of 

 wales on sheet-pile groins and jetties can distribute these forces longi- 

 tudinally, allowing the safe use of smaller structural sections. 



16 



