of the structures. Insufficient data were available to make a judgment on the 

 success of the berms. 



Lower Mississippi Valley Division 



18. The New Orleans District has a unique design problem in that the 

 majority of their jetties are constructed on very soft foundations. It is 

 thought that a majority of the repair and rehabilitation work required on the 

 jetties results from the structures sinking into the foundation. The jetties 

 at Southwest Pass and Mississippi River Gulf Outlet (Figures 18-20), have 

 required considerable repair work due to this subsidence, but it is thought 

 that some of the damage on small localized areas of these jetties is the 

 result of toe slippage. Toe slippage in turn results in downslope slippage of 

 the primary armor resulting in loss of jetty design elevations. Efforts have 

 been made to use toe berms to reduce toe slippage and help prevent foundation 

 slip failures caused by the loading of the jetty construction materials. The 

 berms have provided some additional toe stability, but subsidence of the 

 jetties and slippage of the jetty toes and foundations continue to plague the 

 New Orleans District. 



South Atlantic Division 



Mobile District 



19. The Mobile District has a problem with jetty subsidence but, unlike 

 the New Orleans District's problem, theirs is not thought to be related to 

 low-density foundations. It is generally thought that toe scour is the 

 significant problem after major storms. Bedding layers slough off into the 

 scour holes, and this damage migrates back to the toe of the primary armor. 

 The resulting instability of the armor stone toe leads to downslope migration 

 of the onslope armor and eventual deterioration of the structures. 



20. During the period 1937 to 1938 attempts were made to alleviate toe 

 scour problems on the Panama City Harbor Jetties (Figures 21 and 22) by encas- 

 ing the jetties with asphaltic concrete. Asphaltic concrete mats (2 in. 

 thick) were anchored on the channel side of the jetties and extended over the 

 jetties to a point 24 ft seaward of the existing jetty toe. A hot asphaltic 

 concrete was poured over the matting in an effort to bond the mats together 



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