9. Typical Timber Groin . 



Figure 10 illustrates a typical groin of the impermeable type us- 

 ing marine-treated timber throughout as the construction material. A 

 vertical wall of timber sheet piling is framed into a system of hori- 

 zontal timber wales and round vertical piles to form a tight barrier. 

 The structure is supported laterally by the combined bending strength 

 of the sheet piles and the round vertical piles, all of which derive 

 their fixity from penetration into the earth bottom. The timber wales 

 and the round piles serve to distribute the load from waves traveling 

 along the wall, and thus limit the deflection of the local length 

 loaded at a particular time and prevent opening of the joints between 

 adjacent sheet piles. 



The penetration of the round piles should satisfy two requirements, 

 a rainimiim bearing capacity of 10 tons and a minimum penetration of 10 

 feet. 



The sheet piles are made of two, 3-inch- thick timber staggered to 

 produce a shiplap type of joint between sheets. Losses of material 

 through joints in adjacent sheets are not so critical as in bulkheads. 

 Some groins are deliberately made permeable. However, even if tight 

 joints are desirable to prevent loss of material placed artificially 

 to fill the groin, there is no paving to be undermined as is the case 

 in many bulkheads. The two boards are spiked together for handling 

 purposes and act only as individual planks in bending. 



V. FINGER PIER AND WAVE BARRIER FOR MARINA 



In marinas where the tide range is 4 feet or less, the piers are 

 supported on piling at a fixed elevation. However, for sites with 

 higher tidal ranges, floating piers are used for the greater conve- 

 nience afforded in gaining access to boats. 



A conventional arrangement of pile-supported berthing facilities 

 for small boats in a marina is illustrated in Figure 11. The berths 

 for individual boats are laid out at right angles to, and on both 

 sides of a finger pier. The pier may have a T-head at the outshore 

 end where, as is often the case, the water depth is greater than that 

 alongside the pier proper in order to accommodate the larger boats 

 with deeper draft. 



Figure 12 shows sections through a typical marina pier. Vertical 

 timber planking is used to form a wall for the length of the T-head. 

 This wall acts as a barrier to the passage of short surface waves 

 moving toward shore. In some cases, the vertical planking is driven 

 into the harbor bottom and is supported laterally at the top by the 

 pier structure. If the wave action is only surface chop, the wall does 

 not extend to the harbor bottom; the planks are entirely supported from 

 the pier deck. Section B-B through the pier head indicates a round 



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