and (c) wave-induced displacement of toe berm stone and/or scour of foundation 

 material which results in undermining of the structure's toe. As a result of 

 this displacement, scour, and/or undermining of the structure's toe, the pri- 

 mary armor stone layers become unstable and lead to structural failure. The 

 Portland District carries out repair in these scour areas by filling the scour 

 holes with small stone, core size or smaller, to form a foundation to rebuild 

 the toe and upper portions of the structure. During the repairs and rehabil- 

 itations of the north jetty at Yaquina Bay and Jetty "A" at the mouth of the 

 Columbia River, a sacrificial berm of core-sized material was placed at the 

 structure's toe after the primary armor layers had been placed. It was 

 thought that this material would help stabilize the jetty toes by slowing down 

 the scour rate as well as providing some degree of armoring of the scour hole 

 as the berm stone is displaced into the scour hole. In some instances, scour 

 at the jetty heads has been so severe that it was not economically feasible to 

 try to fill and stabilize the scour holes. The best approach in these cases 

 was to abandon the outer 200 to 300 ft of the jetty heads and rehabilitate the 

 remainder of the structure. 



South Pacific Division 



16. The San Francisco District sited the jetties at Humboldt Bay (Fig- 

 ure 15) as being the only area showing obvious toe stability problems. The 

 channel side of the north jetty and exposed side of the south jetty have shown 

 obvious signs of scour and undermining which resulted in instability and 

 slippage of the dolos toe. Condition surveys of the area have revealed the 

 depths of the scour holes appear to have a seasonal fluctuation. An armor 

 stone berm, extending from 70 to 100 ft out from the existing dolos toes, was 

 included in the jetty repair work conducted in 1985. The multilayered berm 

 consists of a 3- to 6-ton primary armor stone overlying two graded filter 

 layers (Figures 16 and 17). 



Southwestern Division 



17. Several rubble-mound structures in the Galveston District have 

 experienced toe stability problems. Recent attempts to improve stability 

 Include the construction of toe berms of core sized material at the toe 



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