ii.ij.8. One satisfactory method of s ealing an all-stone groin to make 

 it impermeable is to fill the voids between the stones with concrete 

 grouto ThiuS also increases the stability of the structure to resist wave 

 action. The grout should be placed over the entire exposed surface of 

 the groin and forced into the voids to the sand line. A rich mix should 

 be used (? sacks of cement to the cubic yard). If exposed to vjave action 

 x-jhile setting, an admixture of calcium chloride may be added to expedite 

 the set. Where building sand and fresh water are not available, beach 

 sand and sea water have been used satisfactorily. 



hh9o Permeable stone groins differ from impermeable stone groins 

 in -several ways. The permeable groin is constructed with core stone 

 large enough to keep it from being sand and water tight. The side slopes 

 are usually 1 on l§j but the top width is about 3 feetj or the minimum 

 required for stability. The section would be similar to that shown in 

 Fig-ure II4.3. 



k$0o Stone block groins are usually more or less permeable although 

 they have been made impermeable by placing a steel sheet pile diaphragm 

 down the center of the stone blocks. The individual blocks range in 

 weight from 2 to 6 tons but must be of sufficient size to withstand wave 

 action. The height of groin along the profile is easily varied by adding 

 another row of the stone blocks, Tjrpical sections are shown in Figure 

 lUu 



I|.$l. Tiraber Groins. - The most common type of timber groin is an 

 impermeable structure composed of sheet piling supported by wales and 

 round piles. All timbers and piles should be given the maxii-num re- 

 commended pressure treatment of coal tar cresote. All holes should pre- 

 ferably be drilled before treatment. A "tjrpical timber groin is shown 

 in Figure ll|.5. ^he round timber piles forming the priiaary support of the 

 groin should be a minimum of 12 inches in diameter at the butt. 

 Stringers or wales, which are bolted to the piling horizontally, should 

 be at least 8 inches by 10 inches^ preferably cut and drilled before 

 creosoting. The sheet piling is usually either of the Wakefield or the 

 splined type, supported between the wales in a vertical position and 

 secured to the wales with bolts. The plane of the sheeting is vertical. 

 Although usually vertical,, the piling may be driven at an angle in this 

 plane, 



U^2, Aaphal tic Gro ins . ~ A number of attempts have been made to 

 ■use asphaltic materials for groins or jetty construction. Although 

 there have been some notable instances where the asphalt has served 

 the desired purpose i^easonably well^ the experience-. at other locations 

 would indicate very indifferent wsuccess. Accordingly j it is believed 

 the use of asphaltic materials should be given consideration only if 

 large economic advantages appear to justify the risk involved. One type 

 of asphaltic groin that has appeared to afford some evidence of success, 

 has an apron bui].t around it to prevent backwash from undermining the 



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