Ocean City, Maryland (Jachowski, 1959), Nags Head, North Carolina, and 

 Harvey Cedars, Long Beach Island, New Jersey. 



The behavior of sand-ashpalt groins, of the type used to date demon- 

 strates definite limitations of their effectiveness. This is partly due 

 to the limitation of extending the structures beyond the low waterline, 

 and early structural failure of the section seaward of the beach berm 

 crest. The failure in this zone is the result of normal seasonal vari- 

 ability of the shoreface and consequent undermining of the structure 

 foundation. Modification of the design as to mix, dimensions, and 

 sequence of construction may reveal a different behavior. 



6.62 SELECTION OF TYPE 



After planning has indicated that the use of groins is practicable, 

 the selection of groin type is based on varying interrelated factors. 



No universal type of groin can be prescribed because of the wide 

 variation in conditions at each location. A thorough investigation of 

 foundation materials is essential to selection. Borings or probings 

 should be taken to determine the subsurface conditions for penetration 

 of piles. Where foundations are poor or where little penetration is 

 possible, a gravity-type structure such as a rubble or a cellular steel 

 sheet-pile groin should be considered. Where penetration is good, a 

 cantilever- type of structure of concrete, timber, or steel sheet-piles 

 should be considered. 



Availability of materials affects the selection of the type of groin 

 because of costs. The economic life of the material and the annual cost 

 of maintenance to attain that economic life are also selection factors. 

 The first costs of timber and steel sheet-pile groins, in that order, are 

 often less than for other types of construction. Concrete sheet-pile 

 groins are generally more expensive than either timber or steel, but may 

 cost less than a rubble-mound groin. However, concrete and rubble-mound 

 groins require less maintenance, and have a much longer life than do the 

 timber or steel sheet-pile groins. These factors, the amount of funds 

 available for initial construction, the annual charges, and the period 

 during which protection will be required, must all be studied before 

 deciding on a particular type. 



6„7 JETTIES 



6.71 TYPES 



The principal construction materials are stone, concrete, steel, and 

 timber. Asphalt has occasionally been used as a binder. Some structural 

 types of jetties are illustrated in Figures 6-64 through 6-66. 



6.711 Rubble-Mound Jetties . The rubble-mound structure is a mound of 

 stones of different sizes and shapes either dumped at random or placed in 

 courses. Side slopes and stone sizes are designed so that the structure 



6-84 



