whole face of a structure underwent a reduction in elevation as layers, 

 individual bags, and the underlying sand bed were compacted, strengthening 

 the structure, or as torn bags lost sand. Displacement occurred when wave 

 action relocated bags, moving them out of their original position in the 

 structure, then down a face or away from the structure, weakening the area 

 losing bags. Slumping occurred when all the bags from one area of a face 

 slid down the slope, resulting in the undermining of higher bag layers, 

 and further slumping. 



7. Test I. 



a. Construction . The breakwater for test I consisted of 24 bags 

 installed in a 3-2-1, three-layer system designed to produce a submerged 

 breakwater structure 4.5 feet (1.37 meters) high above the sand bed. The 

 bags were dropped into the water during a 3-foot-high, 10-second-period 

 wave condition to test field installation methods. The initial survey 

 after completing construction revealed a uniform structure, but the struc- 

 ture height was only 3.2 feet, 1.3 feet (0.39 meter) lower than expected. 



b. Midtest Tank Draining . Structure I was the only breakwater in- 

 spected during the progress of a test. Surveys during wave conditions a 

 and b indicated that scour was occurring around the structure (Fig. 12). 

 After 2 hours of condition b, the tank was drained for inspection. It 

 was noted that the structure had partially trapped water on the back side 

 and that water was leaking under and through the structure (Figs. 13, 14, 

 and 15). Also, two bags on the bottom layer appeared to be partially 

 emptied. The tank was refilled and wave condition b was continued for 

 another 4 hours to determine if the scour would continue. Subsequent 

 surveys indicated that scour had occurred at the leeward toe, and the 

 breakwater, apparently undermined, had settled during this stage of drain- 

 ing and wave action. The profiles after the additional 4 hours were con- 

 sidered to be the adjusted initial profiles. After these difficulties, 

 the tank was drained only between tests. 



c. Wave and Structure Changes . Waves "peaked-up" as they passed over 

 the submerged breakwater (Fig. 16), but the transmitted wave height was 

 essentially the same as the incident height. In contrast to the slight 

 changes in wave conditions, changes in the structure were significant. 

 Under wave condition a, as a result of settlement and some bag movement, 

 the front slope flattened, the shoreward or back slope steepened, and the 

 crest elevation decreased. During condition b, before the draining of 

 the tank, scour occurred at the rear toe while the front slope flattened 

 and the back slope steepened as much as during wave condition a. During 

 the draining of the tank or the first hour of additional running after the 

 tank was refilled, the entire structure settled, flattening both slopes and 

 reducing the crest elevation. As wave condition b was continued for 3 

 more hours, sand covered the seaward face and a bag on the crest shifted 

 seaward. Both faces settled during wave condition c; however, a bag 

 moved onto the top of the front face and a layer of sand was washed away 

 from the front toe, steepening the front slope. The sand removed from the 



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