the test, commercially marketed bags have been manufactured of nylon coated 

 with various plastics in an effort to reduce damage from exposure to sun- 

 light. During construction of the four test breakwaters, bags were filled 

 in an upright position, then sewn closed, a time-consuming operation. 

 Since the tests, bags have been equipped with a self-sealing opening which 

 allows filling hydraulically while lying flat. During placement, some bags 

 tore when the bucket tried to grip them. The torn bags lost most of their 

 sand filling under wave action. Using modified clamshell jaws with no 

 sharp edges solved handling problems during the last two breakwater tests. 

 Bags are now being made of heavier but more coarsely woven material with 

 increased strength, and can be provided with sewn-in lifting straps if 

 the bags must be dropped into place. The coarse material is more permeable 

 to allow the escape of air or water from submerged or hydraulically filled 

 bags. 



VI. CONCLUSIONS 



1. Sandbag Performance . 



Dropping bags into place through the water in a planned pattern during 

 wave action produced an orderly structure. The structure was lower than 

 expected, but an overestimate of the dimensions of submerged bags had been 

 used for the design. Dispersion of the bags under wave action was deter- 

 mined to be so minor that additional experimental construction under wave 

 action was considered unnecessary. The last two structures, built in still 

 water after the correct submerged bag size was known, were successfully 

 planned and constructed to the design configuration. 



Changes in structure configuration due to bag movement, consolidation 

 of the bags, and settlement into the sand bed were expected, but bag move- 

 ment produced overall changes of such magnitude that the other effects 

 could not be accurately measured. The nylon material was slippery and 

 filled bags were rounded, smooth, and sometimes cushioned by trapped air 

 during the first period of wave attack, preventing adequate interlocking 

 despite the overlapped arrangement of the bags in the structure. The most 

 extensive bag movement occurred during conditions of first wave attack 

 before the loosely placed bags consolidated and, after consolidation, 

 during the steepest wave condition. 



Bag movement was concentrated near the crests of the submerged struc- 

 tures and in the front face of the emergent structure where wave action 

 was most severe. The earliest wave attack removed the top layer of bags 

 from the two highest submerged breakwaters--structure II with a crest 

 submerged at roughly 50 percent of the tank depth and structure III with 

 a crest elevation close to the Stillwater level. Additional bag movement 

 further lowered and widened the crests by removing more bags from structure 

 II and by moving bags in structure III into a pile at the back of the crest. 

 During testing of the emergent breakwater, structure IV with a constructed 

 crest elevation about 4 feet above the Stillwater level, the front face 

 slumped causing loss of both top rows of bags on the crest. Although sand 



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