17 



cylinders were replaced with creosoted piles from 1913 to 1915 and ad- 

 ditional repairs were made in 1921, when all of these structures were 

 examined by diver. The number of cylinders remaining in servicea- 

 ble condition is recorded in the tabulated service records. 



In 1908 an improved type of concrete cylinder was developed in 

 which the concrete was deposited inside of a steel coffer ram which 

 was driven into the bottom and pumped dry. After concreting, the 

 steel shell was pulled and re-used on succeeding cylinders. In this 

 manner the disadvantages of pouring concrete through water were 

 minimized. Piers 36, 38, 40, 39, 26, 28, 30 and 32 were constructed 

 under this system from 1909 to 1914. These piers are giving good ser- 

 vice except for construction defects due to careless workmanship. 

 The principal defects have resulted from the use of excessively wet 

 mixes, from insufficient tamping and failure to properly clean construc- 

 tion joints. Piers 26 and 28 were particularly faulty in respect to 

 construction joints at low water. The upper portions of these cylin- 

 ders were poured on top of an accumulation of laitance and silt which 

 was subsequently washed out and was replaced by grouting. Certain 

 cylinders show signs of disintegration due to excessively wet mixes 

 and lack of tamping. These cylinders have been repaired by encasing 

 them in a 3-inch shell of dense concrete deposited similarly to the 

 "Black Patent" process for concreting piles- The number of repaired 

 cylinders and general condition of the structures are recorded in the 

 tabulated service records. 



A modified type of Holmes cylinder was also developed about 1908 

 and was incorporated in Pier 34 constructed in 1910. In this type a 

 single pile was encased in concrete with special gaskets for sealing the 

 bottom and facilitating the pumping out of the casings. A diver's ex- 

 amination has been made on alternate bents of Pier 34, the results 

 of which are tabulated in the appended service records. No repairs 

 have been made on this pier, which is in good condition after 11 years 

 exposure. 



The Koetitz type of concrete protected pile was also developed 

 about 1908. In this type the green pile was encased in a pre-cast 

 concrete shell, the space between the shell and the pile being filled 

 with sand or grout. Between 1908 and 1910 approximately 250 lin. 

 ft. of concrete bulkhead wharf was constructed on this type of pro- 

 tected pile and in 1911 Pier 17 was constructed entirely on this type. 

 These structures have given good service and are in first class con- 

 dition. The piles in the bulkhead wharves have developed inconse- 

 quential defects in small cracks over the reinfocing of the cylinders. 

 Cracks of this nature are of less import than in the case of reinforced 

 concrete piles, as the casing is largely a protection for the green pile 

 and cracking occurs only above the water line. Neither the structural 

 efficiency of the encased pile nor the protective value of the casing is 

 greatly affected. 



