126 



from the previously dri\en wooden pile o\er which it is afterwards slipped, in place. 

 This process makes appropriate to this form the name, often applied to all pre-cast 

 pile protections, pre-cast concrete jacket. In the other form of pre-cast protection 

 the concrete or mortar covering is fabricated directly upon the untlri\-en pile, o\-er 

 attached reinforcing, and the pile and concrete covering are driven as a unit. Since 

 this covering is usually applied with a cement gun, the name gunite is generally applied 

 to this form of pile. The higher average quality of fabrication made possible by pre- 

 cast construction, as well as the assurance of quality through more effective inspection, 

 are advantages of very real weight. 



The Pre-Cast Pile J.\cket 



Most of this type of jackets have used single, full-length casings, although sec- 

 tional jackets have been designed with special details for connecting the sections as 

 they were lowered into position. The patent, in fact, taken out by F. A. Koetitz, 

 by whose name the single-piece pre-cast pile jacket has come to be called locally, was 

 for a special design of pre-cast sectional pile jacket, rather than the more widely 

 used single-piece form. The pre-cast sectional concrete jacket has ne\'er attained any 

 popularity in this region. 



Pre-cast concrete pile jackets may be round, octagonal, square, or of any other 

 desired external section; inside they are usually round and of enough greater diameter 

 than that of the pile to allow for irregularities in the latter and for the insertion between 

 pile and jacket of a pipe with which to pump out and grout the space. The minimum 

 thickness of shell is usually 2 1-2 to 3 inches. When the wooden pile is driven at the 

 time that the concrete protection is to be applied, if the bottom is soft, there may be 

 fastened to the pile, at a point which will be several feet below mud line, blocks upon 

 which the concrete cylinder w411 rest. 



Pre-cast jackets of this type were first used on the San Francisco waterfront in 

 1908, and between that time and 1911 approximately 300 were constructed, chiefly 

 in bulkhead wharves. 



In 1911, Pier 17 at San Francisco was built on 1130 of these piles. The cylinders 

 used were 26 inches in diameter, outside dimensions, and the walls were 3 inches thick. 

 They were driven about 8 feet into the mud and extend upward to the underside of 

 the steel deck beams. The wooden piles were cut oft" at about mean sea level, and the 

 cylinders above the heads of the piles were filled with concrete, into which the beams 

 were anchored by steel bars. The space between the wood and concrete was filled 

 with sand in the early part of the work, but later a grout filling was used. 



The condition of these piles at the present time is e.xcellent. A careful examination 

 from a boat showed no defects above low water. In 1921, a diver made an examination 

 from low water to the mud line of 50 piles selected at random and covering the entire 

 length and width of the pier. No defects of any kind could be discovered. Of the 

 several hundred of these piles driven in bulkhead wharves along the San Francisco 

 waterfront between 1907 and 1922, some are now showing small defects but the 

 majority are in good condition and all are still in service. 



The success of these early installations has resulted, after a considerable period 

 of quiescence, in a renewed adoption of this protection. It was used in the new Pier 50 

 whose construction was commenced in 1925 by the Board of State Harbor Commis- 

 sioners in San Francisco. It was also used in the same year by the Alaska Packers 

 Association in the Encinal Terminal wharves in Alameda and by the Harbor Commis- 

 sion of San Diego in the construction of a pier and a bulkhead wall for tideland 

 reclamation. 



