3. Dry and Submerged Weight Test . 



a. Test Conditions . Six identical-sized sand-filled bags were weighed 

 while submerged to determine the typical weights o£ bags used in the break- 

 water tests and the effects of submergence depth and material weight on 

 time-dependent changes in the volume of trapped air. Two different weights, 

 or weaves, of nylon material were tested, the heavier material with a 

 "tighter" weave (Table 1). Three bags of each material were weight-tested, 

 although only the light-material bags were used in the breakwater tests. 

 One light-material bag and one heavy-material bag were submerged in fresh- 

 water at a depth of 7.5 feet (2.29 meters). The other four bags were 

 submerged at a depth of 5 feet. 



b. Test Procedure . The test procedure began by filling the bags with 

 sand. As in the breakwater tests, each bag was filled with damp sand from 

 an overhead hopper until about 75 percent full, sewn closed, stockpiled, 

 and placed in a metal basket suspended by cables from a dynamometer. After 

 determining the dry and submerged tare weight of the basket, the dry weight 

 of the bag was recorded, and the apparatus was suspended from a steel 

 I-beam to the proper water depth. The submerged weight was recorded at 

 various time intervals (Table 2). 



At the end of the test period, the air bubble in each bag (except bag 

 1) was punctured and, after at least a 5-minute wait, the final bag weight 

 in water was recorded. The test apparatus was removed from the tank and 

 the water-saturated weight in air was recorded. 



c. Bag Weights . The bag weights in air and at the end of the submer- 

 gence tests are recorded in Table 3. The weights at certain times during 

 the submergence tests were recorded for bags 2 to 6 in Table 2. Data from 

 the first test, using a light-material bag, were erratic during the middle 

 of the test due to a malfunctioning dynamometer, and are not included in 

 Table 2. Weights from the beginning and end of the test were close to 

 values from other tests (Table 3). The average dry weight was 2,447 pounds 

 (1,110 kilograms) for the three light-material bags, 2,812 pounds (1,275 

 kilograms) for the three heavy-material bags, and 2,629 pounds (1,193 

 kilograms) for all six bags. No reason is known for the consistently higher 

 weights of the sand- filled, heavy-material bags. The difference in the 

 weights of empty bags of the two materials is only about 0.2 pound (90 

 grams) . 



A plot of submerged bag weights versus time (Fig. 3) shows that the 

 largest changes occurred during the first 30 minutes of submergence, then 

 the weights slowly approached stable values. Although differences among 

 the final submerged weights before puncture corresponded to differences 

 among the dry weights, no relationship to differences in material or depth 

 of submergence was apparent. The final submerged weight before puncture 

 appeared to be the stable weight for bags undisturbed during air leakage, 

 and the submerged weight after puncture could be used to estimate the final, 

 inplace weight of bags buried within a structure. The average submerged 



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