146 



Asphalt coatings, as described previously for harbor exposures, will undoubtedly 

 be beneficial in prolonging the life of these structures; but owing to the se\-erit>' of 

 wa\'e wash and the cutting action of sand, it is believed that more resistant coatings 

 are justified. Steel shell protection from low water to the deck line is suggested as a 

 feasible protection for this exposure. Steel jackets of ^i^-inch lioiler plate have been 

 in ser\-ice on San Francisco Harbor for twent\--fi\-e years and similar slu-Us of 3|g-iiich 

 or 14-inch material should give ser\-iccable, if not equally long, life in "ocean" wharves. 

 Concrete encased piles ha\'ing a minimum of steel to rust are also advantageous under 

 conditions of se^•erc corrosion action. The decks should be so designed as to thoroughly 

 brace the structure. Steel jacketed piles, either of solid concrete or composite con- 

 struction, painted structural steel members encased in concrete, and galvanized or 

 painted reinforcing bars of small dimension are suitalile structured comjjonents for 

 "ocean" wharves, considered from the viewpoint of corrosion and deterioration. 

 There are, of course, ocean locations where the shock of waves and the shifting of 

 bottoms are such that no structure of a wharf t\pe should be constructed, and failures 

 due to such storm conditions should not be confused with failure due to sea water 

 action on concrete, wood and steel. 



Constructing and Driving Concrete Piles 



The size and reinforcement of concrete piles depend upon the length of pile to 

 lie handled. The quantity' of steel should be the mininumi which will permit careful 

 handling without cracking. Experience has shown that piles of square cross section 

 should range from about 16x16 inches with four ^^-inch bars, for piles of 50 feet 

 length or under, to 20x20 inches with six 1-inch bars for piles 100 feet in length. The 

 specified thickness of protecti\e concrete coating should be pro\ided above the tide 

 line. While circular shaped piles are preferalile to rectangular shapes for resisting 

 impacts of floating debris and the internal pressure of rusting steel, the additional form 

 cost does not warrant their use. Rectangular piles should be rounded or bevelled at 

 the corners. In handling, piles from 50 to 80 feet long should be evenly supported at 

 not less than four points; piles longer than 80 feet at five or more points. 



Reinforced concrete piles should be driven with a steam hammer properly 

 cushioned In' means of wood or rope set in a suitable driving cap. The hammer 

 specified (5000 lbs. falling three feet) is a standard size which is usually available, 

 but piles of one-to-fi\e concrete of the quality specified will resist the heaviest driving 

 of a 7500-lb. hammer falling 42 inches, without injur^•, and this size is preferable for 

 heavy piles 80 feet or more in length. When driven in sand substrata, a water jet 

 should be used in conjunction with the steam hammer to secure penetration. Re- 

 inforced concrete piles are subject to cracking in the portion above the water line, by 

 reason of their rectangular shape and the heavy steel required for handling. In "har- 

 bor" exposed structures, this disintegration is confined to narrow limits just above 

 high tide line and is readily repaired by coating with mortar or additional concrete. 

 It can be retarded, if not entireh- pre\ented, 1)\- coating with asphalt. In "ocean" 

 exposed surfaces, this disintegration is serious, because of its greater extent and rapidity 

 and the more difficult repair conditions, as previously mentioned. 



Pre-cast shells for concrete jacketed piles should be designed with just enough 

 steel to enable handling and placing without cracking and injur\-. The depth to 

 which the casing should be carried depends upon the possible scour at the site from 

 currents and future dredging. Circular shells from 18 inches to 26 inches in diameter 

 and from 2 to 3 inches in thickness have proved satisfactory, and shells 26 inches in 

 diameter and 65 feet in length have been successfully installed. 



