31 



We have nothing new that would change the conclusions appearing 

 therein, which are summarized at the end of this report. Piles treated 

 with the better types of coating will always find a place in semi-tem- 

 porary marine construction- It should, however, be added that, since 

 the cost of paint and batten coatings is greater per linear foot applied 

 than is that of creosote treatment, the lower cost per pile of the former 

 mehod, which is usually assumed as compared with the latter, is condi- 

 tioned by the relative length of water section of the pile, decreasing as 

 the latter increases, especially when the increased water depth is ac- 

 companied by decreased bottom driving depth. 



Concrete Protections 



The report of 1921 described in considerable detail the numerous 

 types of concrete protection which have been utilized on San Francisco 

 Bay. These types are characterized by various ingenuities in apply- 

 ing the protection, but they may be roughly classified in two general 

 groups, pre-cast protections and cast-in-place protections. 



The principal representative of the pre-cast group hitherto used 

 on San Francisco Bay is the Koetitz pile in which type the untreated 

 pile is surrounded with a concrete shell, cast separately and set in place 

 after the pile has been driven. (Plate 1, Fig. 2; Plate 2, Fig. 1.) 



The cast-in-place group includes the various simple methods of 

 concreting piles between the tides, the encasing of piles with steel 

 shells or pipes filled with concrete, the Holmes patent for depositing 

 concrete in a wooden casing driven into the bottom, and the various 

 modifications for lowering the plastic concrete casing down the pile as 

 the depositing of plastic concrete proceeds. (Plate 2, Fig. 2; Plate 2, 

 Fig. 1.) 



During the year a new process has appeared which is sufficiently 

 unique to require separate classification and may become the proto- 

 type for a third group. This is the Newsom-Squire pile which is cast 

 simultaneously with the driving of the pile and which utilizes the 

 impact of the pile hammer both for securing penetration in the bottom 

 and for compacting the plastic concrete. 



The service records which have become available confirm last 

 year's favorable report on the excellence of pre-cast protections of the 

 Koetitz type. Piles of this type have been exposed for twelve years in 

 trulkhead wharves and for ten years in Pier 17 of the San Francisco 

 Waterfront without a single repair or replacement and with no visible 

 deterioration other than a few small cracks above the high water 

 line. 



With reference to cast-in.place protections, attention is directed 

 co the long service obtained from the steel shell cylinders of Piers 5 

 and 20 which have been in place for approximately twenty-five years. 



