120 



is being attacked. The details of the forms, reinforcement and methods vary con- 

 siderably. The forms are usually left permanently in place. 



The Ci'LVERT Pipe Method 



This form of construction has been used at two places on San Francisco Bay and 

 is reported to have been used recently at two places on the Oregon coast. It consists 

 of slipping a corrugated iron culvert pipe over the end of the pile, forcing the former 

 as deeply as practicable into the sand or mud and filling the space between the pipe 

 and the pile with concrete. This method has not been used recently in this region, 

 and the Committee has not learned just how the work was done on the Oregon coast. 

 Other cylinder forms, as well as ordinary box forms, have been used in this type of 

 process. Reinforcement, if used, may be in the form of rods, wire mesh or spikes 

 driven into the pile, or it is sometimes omitted altogether. No data are yet available 

 on the cost of this process, or the durability of the pipe and concrete. 



The effectiveness of the method will depend upon the life of the casing, the quality 

 of the concrete and the success in getting the protection deep enough into the bottom 

 to avoid danger from a changing mud line. This method is entirely feasible where the 

 mud is exposed at low tide and where, on account of the relative shortness of the 

 protection and the fact that the mud is exposed at low water, the workmen can see 

 their work and it should be possible to obtain good concrete. The necessity of working 

 between tides, however, requires considerable speed, with the accompanying danger of 

 sacrificing quality. When the protection is thus exposed at low tide, it is also an easy 

 matter to inspect it and to keep it in good repair. The deeper the water, the less practi- 

 cable the method becomes because of the increasing difiiculty already mentioned of 

 making the forms watertight and thus avoiding the uncertain quality of concrete 

 formed by dropping it through water, of obtaining such a relatively thin shell of 

 satisfactorily even thickness, and of securing proper reinforcement of this shell. 

 Thorough inspection is also rendered more difficult. The specific installations of 

 this general type, of which the Committee has record, are as follows: 



The city of Alameda in 1914 built a pipe line trestle about 1400 feet long, consisting 

 of two-pile bents spaced 15 feet apart. The piling used for the initial construction was 

 Douglas fir, protected by a coating of asphaltic tar, burlap and redwood battens. 

 After a short time this protection proved ineffective against the attack of Limnoria, 

 and it was decided to encase the piles in concrete. Metal forms were placed at low 

 tide, the concrete poured and the forms subsequently removed. The cost of this work 

 is reported to have been S4,000, with labor at S2.50 per day. This amounted to an 

 average cost of about $22 per pile. In December, 1920, the piles were examined, at a 

 time when about half of them were exposed down to the mud line. The concrete on 

 eight was found to be disintegrating. Untreated wood at the bottoms of four was being 

 exposed to borer attack; and the covering had not been placed high enough in six 

 cases, so that Limnoria was working above it. 



In March, 1919, the U. S. Naval Training Station repaired 20 damaged piles at 

 Yerba Buena Island, 16 ins. in diameter by placing No. 16 gauge galvanized iron forms 

 30 ins. in diameter around them and filling with concrete. The concrete was reinforced 

 by No. 10 gauge 4-in. wire mesh secured to the wood and held 2 inches from it by No. 40 

 spikes. The average cost, including labor and material, was S2.00 per lineal foot. 

 Insufficient time has elapsed to indicate the effectiveness of this protection. 



