weight after puncture was 1,373 pounds (623 kilograms) for two light- 

 material bags, 1,565 pounds (710 kilograms) for three heavy-material bags, 

 and 1,488 pounds (675 kilograms) for all five bags. Both light- and 

 heavy-material bags gained 80 pounds (36 kilograms) or more immediately 

 after puncture; however, the total weight gained during. submergence, from 

 the initial value to the value after puncture, was a maximum of 235 pounds 

 (107 kilograms) for the light-material bags (bag 3) and 325 pounds (147 

 kilograms) for the heavy-material bags (bag 4). 



d. Air Retention . The ratio between the submerged and dry bag weights 

 was a measure of the proportion of air trapped in a bag. The change of 

 the ratio with time for five bags is plotted in Figure 4. If the specific 

 gravity of the damp sand in the dry bag is assumed to be 2.65 and the 

 specific gravity of the bag itself is neglected, the ratio of submerged to 

 dry weight for a submerged bag with all air replaced by water would be 

 0.623. The ratio immediately before puncture averaged 0.545 for the light- 

 material bags and 0.532 for the heavy-material bags. The light-material 

 bags contained a slightly smaller proportion of air when the bag weight 

 stabilized. 



The rate at which a bag approached a stable condition was measured by 

 considering the asymptotic behavior of the change of weight with time and 

 assuming that the bag weight stabilized when it reached 99 percent of the 

 final prepuncture submerged weight. The time required to reach stability, 

 tg, is given for bags 2 to 6 in Table 3. The light-material bags stabil- 

 ized in less time than the heavy-material bags, and the bags submerged 

 7.5 feet stabilized faster than the bags submerged 5 feet. The maximum 

 tg was 17 hours for a heavy-material bag at a 5-foot depth; the maximum 

 for a light-material bag was only 2.2 hours at the same depth. Although 

 the heavy-material bags held more sand when filled to 75 percent of capac- 

 ity, the light-material bags used for the breakwater tests reached a stable 

 submerged weight more quickly and contained a smaller proportion of air 

 when stable. 



III. BAG BREAKWATER TESTS 



1. General . 



Four sandbag breakwaters were built and tested to determine structure 

 stability and wave attenuation. Tests were conducted at full scale on a 

 sand bed in 12 feet (3.66 meters) of water (Fig. 5). Structures I and 11 

 were 3.2 and 7 feet (0.98 and 2.13 meters) high above the sand bed, respec- 

 tively; each structure had one row of bags along its crest forming a crest 

 width of approximately 7 feet. Structures III and IV were 12.1 and 16.4 

 feet (3.69 and 5 meters) high, respectively, and each had two rows of bags 

 along its crest forming a crest width of approximately 14 feet (4.27 meters) 



Many aspects of the testing program were planned to represent prototype 

 conditions. The breakwaters were built in layers by dropping bags through 

 water onto a sand bed. Wave attenuation was determined by comparing wave 



