With a significant wave 14 feet high (expected to occur every 2 years) some overtopping 

 occurred in the model. During these tests, gravel at the toe underlying the rock was in 

 continuous motion. 



With a significant wave 17.5 feet high, the entire slope slumped after the first few waves. 

 There was a high degree of overtopping and considerable force and pressure against the 

 seawall; cover stone was removed, exposing gravel and undermining the wall. 



Due to infrequency of a 17.5-foot wave, design size of protective riprap was not changed. 

 Because of salinity of water at site, it was recommended that stone size be increased by 10 

 percent. 



(3) Instrumentation and Observation (U.S. Army Engineer District, Norfolk, 1971). 

 A wave gage has been installed on the fishing pier off Portal Island No. 1 by CERC (Fig. 1). 



Settlement plates are distributed over the finished grade area of the islands (and within 

 the tunnels) for checking settlement by the Bridge and Tunnel District. 



Rows of pins are set in the armor stone, transversely across the islands, Nos. 1 and 3, for 

 checking horizontal and vertical movement of the armor stone. This is carried out by means 

 of surface surveys by the U.S. Army Engineer District, Norfolk, and checked by aerial 

 surveys. Underwater surveys are accomplished for checking armor stone movement and 

 changes in bottom topography near the structures. 



Extensive hydrographic surveys are also performed over the entire project by the Bridge 

 and Tunnel District. 



g. Structural Performance (U.S. Army Engineer District, Norfolk, 1971; Sverdrup and 

 Parcel, 1972). Structures are performing satisfactorily, except that one island has 

 experienced some settlement (up to 2 feet at one end) due to localized foundation 

 conditions. Design wave heights and winds have not been experienced to date. Structures 

 have experienced no damage from environmental conditions; hence, no repair work has been 

 necessary. Maintenance has not been performed and none is planned. 



Regular surveillance has been performed on the armor stone. The results indicate Uttle or 

 no horizontal or vertical movement. Aerial photos, checked by surface survey, cover 

 above-water areas, and hydrographic surveys cover underwater areas. 



The finished grade of all islands was surfaced with asphalt to prevent wind erosion of 

 sandfiU shortly after construction. Routine maintenance of the surface is required at several 

 locations. 



Splash walls are still in good condition except for an isolated area (Sverdrup and Parcel, 

 1972). Stabilization of the wall at this point is being considered. 



There have been several incidents of ships or barges coUiding with the trestle part of the 

 project, involving repair work consisting of new piles and replacement sections, ordinarily 

 held in stock. There are no records of the islands being hit. 



h. Effect of Structures on Environment. 



(1) Physical. The bottom topography in the vicinity of the islands has changed 

 between the regular hydrographic surveys by the Corps of Engineers with a general pattern 



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