arch-web sections. The round pile and timbers should be creosoted to the 

 maxiraum pressure treatment for use in waters with marine borers. 



Figure 6-56 illustrates the use of a cantilever-steel sheet-pile groin. 

 A groin of this type may be used where the wave attack and earth loads are 

 moderate. In this structure, the sheet piles are the basic structural 

 members; they are restrained at the top by a structural-steel channel welded 

 to the piles. Differential loading after sediments have accumulated on one 

 side is an important consideration for structures of this type. 



The cellular-steel sheet-pile groin has been used on the Great Lakes 

 where adequate pile penetration cannot be obtained for stability. A cellular- 

 type groin is shown in Figure 6-57. This groin is comprised of cells of 

 varying sizes, each consisting of semicircular walls connected by cross dia- 

 phragms. Each cell is filled with sand or aggregate to provide structural 

 stability. Concrete, asphalt, or stone caps are used to retain the fill 

 material . 



c. Concrete Gr oins . Previously, the use of concrete in groins was gen- 

 erally limited to permeable-type structures that permitted passage of sand 

 through the structure. Many of these groin designs are discussed by Portland 

 Cement Association (1955) and Berg and Watts (1967). A more recent develop- 

 ment in the use of concrete for groin construction is illustrated in Figure 

 6-58. This groin is an impermeable, prestressed concrete-pile structure with 

 a cast-in-place concrete cap. At an installation at Masonboro Inlet, North 

 Carolina, a double-timber wale was used as a cap to provide greater flexi- 

 bility. Portland Cement Association (1969) and U.S. Army, Corps of Engineers 

 (1971b) provide guidance on concrete hydraulic structure design. 



d. Rubbl e-Mound Groins . Rubble-mound groins are constructed with a core 

 of quarry-run material, including fine material to make them sandtight, and 

 covered with a layer of armor stone. The armor stone should weigh enough 

 to be stable against the design wave. Typical rubble-mound groins are 

 illustrated in Figure 6-59. 



If permeability of a rubble-mound groin is a problem, the voids between 

 stones in the crest above the core can be filled with concrete or asphalt 

 grout. This seal also increases the stability of the entire structure against 

 wave action. In January 1963 asphalt grout was used to seal a rubble-mound 

 groin at Asbury Park, New Jersey, with apparent success (Asphalt Institute, 

 1964, 1965, and 1969). 



e. Asphalt Groins. Experimentation in the United States with asphalt 

 groins began in 1948 at Wrightsville Beach, North Carolina. During the next 

 decade, sand-asphalt groins were built at the following sites: Fernandina 

 Beach, Florida; Ocean City, Maryland (Jachowski, 1959); Nags Head, North 

 Carolina; and Harvey Cedars, Long Beach Island, New Jersey. 



The behavior of the type of sand-asphalt groin used to date demonstrates 

 definite limitations of their effectiveness. An example of such a structure 

 is a groin extension placed beyond the low-water line which is composed of a 



6-83 



