piers, cofferdams, or caissons. Unlike 

 individual piles, use of sheet piles nor- 

 mally will not result in an open struc- 

 ture. 



Structure Functions 



A pier usually functions as a land- 

 ing and mooring place for vessels. Such 

 a pier might also be used for loading or 

 discharging cargo. Another function is 

 to provide access to deep water from 

 land. This is usually in conjunction 

 with a landing or mooring place. A pier 

 can also be used for boat launching and 

 retrieval by means of a hoisting mech- 

 anism located on the pier. A pier may 

 also provide recreational usage, as for 

 fishing or sight-seeing. Used for these 

 purposes, a pier might also serve as a 

 platform for restaurants or other com- 

 mercial ventures. 



Separately or in clusters, pilings 

 can perform several functions including: 



o Mooring vessels, anchoring floating 

 rafts or floating platforms (Figure 

 40); 



Supporting aids to 

 as lights, ranges, 

 channel markers, 

 (Figure 41); 



navigation, such 

 day markers, 

 or reflectors 



o Serving as the fenders or protec- 

 tive features for piers, landings, 

 bridges, or other structures. 



Pilings are also the basic element 

 in many larger structures used for the 

 mooring vessels and providing coastal 

 protection. 



Si te Characteristics and Environmental 

 Conditions 



Piers extend into the water from a 

 bulkhead or from the natural shoreline. 

 They may extend in different directions 

 to various depths, depending on naviga- 

 tional requirements or their designated 

 function. The location of a single pile 

 or piling is also dependent on function. 



Piers, pilings, and pile-supported 

 structures frequently occur with the 

 marinas which are often located in estu- 

 aries and bays. 



Placement Constraint s 



Engineering. A typical residential 

 fixed pier is 40 to 60 ft (12 to 18 m) 

 in length. For a marina complex it is 

 common for a pier to extend 2C0 to 250 

 ft or 61 to 76 m (Carstea et al. 1975). 

 Piers may be straight or have "L" or "T" 

 configurations (Figure 42). 



Piles are driven to a depth which 

 will provide stability. This depends on 

 the bottom characteristics of the site, 

 as well as the lateral forces working 

 against the structure. For example, a 

 pier used for mooring purposes would be 

 subjected to the forces of a vessel 

 striking the side and would, therefore, 

 have to support a greater lateral load 

 than a pier used solely for fishing. 

 The length of pile extending above the 

 water is dependent on wave height and 

 tide. According to Carstea et al. (1976) 

 enough pile should be exposed to allow 

 the decking to remain at least 3 ft (0.9 

 m) above the water and provide 3 to 4 ft 

 (0.9 to 1.2 m) for mooring or handrails. 



Pile dimensions vary greatly. A 

 mooring pile is usually around 10 in (25 

 cm) in diameter with 8 to 10 ft (2.4 to 

 3.0 m) exposed above mean high water 

 (Carstea et al. 1975a). A dolphin is 

 usually constructed with a center pile 

 approximately 12 to 14 in (30.5 to 35.6 

 cm) in diameter, surrounded with piles 

 from 8 to 10 in (20.3 to 25.4 cm) in 

 diameter. A heavy wire rope is generally 

 used to bind them together (Carstea et 

 al. 1975a). 



Wood pilings should be treated to 

 prevent decay and destruction due to 

 marine borers (Figure 43). Treatment 

 may include toxic surface coatings, pile 

 sheathing, or creosote-coal tar impreg- 

 nation. In areas where gribble, Limnoria , 

 and marine clam, Pholas , attack are com- 

 mon, the American Wood-Preservers' Asso- 

 ciation (AWPA) C3 Standard recommends a 

 dual treatment for wood pilings (Henry 

 and Webb 1974). The addition of an 

 insecticide may retard infestation 

 (Lindgren 1974). Methods of protection 

 are updated by the AWPA and should be 

 consulted periodically. 



An open-pile structure is recom- 

 mended over a solid-fill structure. The 



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