when subjected to blows from the waves and provide positive sand-tight 

 connections between adjacent piles. The type of pile selected is 

 governed by the wave action to be encountered. The section modulus in- 

 creases as the depth of the arch increases in the arch webj M, and Z 

 sections. The steel sheet pile groin 'is usually constructed with 

 steel or horizontal timber wales alon§ the top of the steel pile and in 

 some cases J vertical round timber piles or brace piles are bolted to 

 the outside of the wales for added support. The round piles are not 

 always required with the M and 2 sections but would ordinarily be used 

 with the flat or arch xreb sections e A typical design for a steel sheet 

 pile groin is shown in Figure lUl, The round pile and timbers should be 

 creosoted to maximum treatment for use in waters infested with marine 

 borers. This would not be as necessarj in the Great Lakes, In some in- 

 stances the life of the steel sheet pile has been indefinitely prolonged 

 by pouring concrete slabs on either side of the sheet pile after holes 

 have been scoured through the piling by moving sand. 



UUJ' The cellular tjj>e of steel sheet-pile groin is being used 

 more extensively, especially on the Great Lakes where foundation conditions 

 are a problem and adequate pile penetration cannot be obtained, A typical 

 cellular type groin is shown in Figure 1^2, 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 increase 

 stability, A concrete slab may or may not be poured over the top to 

 provide a walkway or platform and to retain the fill material, 



kh^o Stone Groi ns. - Stone groins have been successfully constructed 

 of either rubble or of cut stone blocks . Either type can be made per- 

 meable or impermeable. The impermeable rubble-stone groin is constructed 

 with a core of quarry run stone including sufficient fine material to 

 make it sand tight^ and with caps of stone sufficiently . heavy to protect 

 the structure from anticipated wave damage. The ^random or rubble-stone 

 mound is usually constructed with 1 on ij side and end slopes and a top 

 width of 5 feet or more, A typical stone groin is shown in Figure lU3. 

 The size of stone used in the core may vary depending upon the source. 

 The layer of cover stone should be a minimum of 3 feet thick with in- 

 dividual stones weighing from 1 to U tons or more depending on the 

 wave action to be resistedj averaging approximately 3 tons, 



UU7, Several variations to the all-stone groin have been used. In 

 some instances j( to increase the impermeability of the structure, a diaphragm 

 of timber Wakefield piling or steel sheet piling has been included. Also 

 in many instances the shore end of the structure has been constructed 

 either of timber or steel sheet piling, thus reducing the overall cost 

 of the structure without reducing its economic life or its ability to 

 resist severe wave attack or erosion. Generally the timber or steel 

 section does not extend seaward of the crest of berm. Where it is not 

 exposed to the action of marine borers, untreated timber may give a con- 

 siderable length of service, 



211 



