WAVE IMPACT ON ENGINEERING 

 STRUCTURES 



THE failure of a breakwater, formed of blocks of masonry or 

 concrete, under wave impact, is usually initially due to under- 

 mining or settling of the foundations, or to the displacement 

 of some one or more of the face blocks, this permitting free 

 access to the interior of the mass. Once any such serious 

 displacement has taken place, total failure is usually a matter 

 of comparatively short time. 



As is a well-known fact, the normal impact of a wave on 

 the face or top of such a structure may produce the with- 

 drawal of a block weighing several tons, the motion of the 

 block being in the opposite direction to that of impact. 



Thus at Ymuiden, a ' header ' block in the seaward face 

 of the pier, measuring 7 ft. in length and presenting a face to 

 the waves of 4 ft. by 3 ft. 6 ins., was started forward to the 

 extent of 3 ft. by the stroke of a wave compressing the air 

 behind it. 1 This block weighed about seven tons, and the top 

 of it was at the level of low water. It had three courses of 

 concrete blocks, each 3 ft. 6 ins. in thickness, resting upon the 

 top of it. These were all set in Portland cement mortar, but 

 the course to which the block in question belonged was built 

 dry, as were those below it. A similar instance was noticed 

 at East London (Cape Colony) where several adjoining blocks 

 were forced outwards on the harbour side of the breakwater 

 during a storm. 2 Another example of this was noticed by 



1 This description is from Shield's Principles and Practice of Harbour Construction* 

 p. 83. The italics, however, are the author's. 



2 Wm. Shield, Harbour Construction, p. 109. 



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