of sheet-piles depends on the earth forces to be resisted. Where the 

 forces are small, straight web piles can be used. Where forces are great, 

 deep-web Z piles should be used. The timber-steel sheet-pile groins are 

 constructed with horizontal timber or steel wales along the top of the 

 steel sheet-piles, and vertical round timber piles or brace piles are 

 bolted to the outside of the wales for added structural support. The 

 round piles may not always be required with the Z pile, but ordinarily 

 are used with the flat or arch web sections. The round pile and timbers 

 should be creosoted to maximum treatment for use in waters with marine 

 borers. 



Figure 6-60 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. 



The cellular type of steel sheet-pile groin is used on the Great 

 Lakes where adequate pile penetration cannot be obtained for foundation. 

 A typical cellular type groin is shown in Figure 6-61. This groin is 

 comprised of cells of varying sizes, each consisting of semicircular walls 

 connected by cross diaphragms. Each cell is filled with sand or stone to 

 provide structural stability. Concrete, asphalt, or stone caps are used 

 to retain the fill material. 



6.613 Concrete Groins . Previously, the use of concrete in groins was 

 generally limited to permeable-type structures that permitted passage of 

 sand through the structure. Many of these groins designs are discussed 

 by Portland Cement Association (1955) and Berg and Watts (1967). A more 

 recent development in the use of concrete for groin construction is illus- 

 trated in Figure 6-62. This groin is an impermeable, prestressed concrete- 

 pile structure with a cast-in-place concrete cap. At a more recent instal- 

 lation at Masonboro Inlet, North Carolina, a double timber wale was used 

 as a cap to provide greater flexibility. 



6.614 Rubble-Mound Groins . Rubble-mound groins are constructed with a 

 core of quarry-run material including fine material to make them sand- 

 tight, and covered with a layer of armor stone. The armor stone should 

 weigh enough to be stable against the design wave. A typical rubble- 

 mound groin is illustrated in Figure 6-63. 



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

 between stones can be filled with concrete or asphalt grout. This sealing 

 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, 1969.) 



6.615 Asphalt Groins . Experimentation in the U.S. with asphalt groins 

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

 decade, sand-asphalt groins were built at Fernandina Beach, Florida, 



6-83 



