130 



tween high water level and the wharf deck. In this portion of the pile they are easily 

 observed and repaired, as contrasted to deterioration below low water which cannot 

 easily be observed. 



As a result of experiments and obser\ations, the engineers of the Harbor Board are 

 confident that in all future construction, deterioration due to rusting of embedded 

 steel can be retarded, if not entirely prevented, by certain simple expedients, such as 

 embedding the steel deeper in the concrete in the section above low water, having 

 about three inches of concrete co^'ering between the steel and the pile surface; using 

 galvanized steel; periodically coating the concrete surface with asphalt, paraffine or 

 other waterproofing. 



Square piles have been used exclusi\ely in San Francisco work, the size varying 

 from 16 inches square for lengths up to 45 feet to 20 inches for lengths up to 105 feet. 

 The ]")oints are tapered down on two sides for a distance of from 6 to 10 feet to a width 

 of 10 inches. The reinforcement consists of square corrugated bars with spiral wrapping 

 of No. 3 wire. The amount of steel varies according to the pile length from four 

 5'4-inch to six 1-inch bars. 



In making concrete piles, the established practice is to use a mixture of one part 

 cement to five parts aggregate. The different sizes of aggregate, usually four, are 

 brought on the ground separateh- and proportioned so as to obtain as dense a mixture 

 as possible. Thorough mixing and tamping are required and the mortar is spaded 

 against the forms. All piles are cured at least 45 days before driving. Piles up to 90 

 feet in length are lifted by a 4-point suspension — the cables being attached at the 





Pit^l!!' 



Fig. 50. Handling and dri%ing pre-cast concrete piles, Berth 2M), Los Angeles harbor. 



center of each quarter of the pile; those over 90 feet long are lifted by a 5-point sus- 

 pension, or at the center of each fifth of the pile. Driving is done with a heavy steam 

 hammer, assisted by water jetting where necessary. 



Some of the advantages possessed by this t\pe of construction are the rigid, 

 substantial substructure which results and the possibility of the use of a permanent, 

 fire-proof superstructure. The certainty of securing more careful inspection and work- 

 manship of pre-cast piles built on land makes them more satisfactory than cast-in- 

 place concrete cylinders. The objections to this type of construction are the high 

 first cost and the length of time required for construction of the pile; the high cost of 



