19 



have been subjected to Limnoria attack. This is done with cement 

 mortar which is forced into the holes and then pointed with plaster 

 of paris to protect the cement mortar from the tide. A record of all 

 piers repaired is given in the tabulated service tests. In general it 

 may be stated that 80% of the abrasions attacked are produced by 

 pile dogs; about 15% by checks developed during or since driving and 

 the balance from miscellaneous defects. In some of the repaired 

 piers (19, 21, 25 and 27) steel staging bolts were used which were with- 

 drawn without pluging the holes. These openings were heavily at- 

 tacked. In all cases the piles of the repaired piers on the north side 

 of the Ferry Building contained larger holes and were more heavily 

 attacked than the piles in the new piers to the south. This is possibly 

 due to the increased abrasion of the piles where driven through the 

 roof and deck of existing work as compared with the unobstructed work 

 on new piers. It was impossible to patch the inaccessible portion of 

 the piles below the water line, but judging from the extent of the at- 

 tack which is visible it is thought that the stability of the piles will 

 not be appreciably reduced for at least another six year period, at which 

 time a percentage of the piles must be repaired or replaced. Xylotrya 

 or Teredo attack was visible only where piles had been split or checked; 

 in these cases it was more rapid and serious than the Limnoria attack 

 in small abrasions. 



In 1911 pre-cast reinforced concrete piles were introduced in the 

 Bulkhead Wharf of Pier 17. This construction has been adopted for 

 all succeeding bulkhead wharf construction aggregating approximately 

 8500 feet of bulkhead. Following the destruction of Pier 46 by fire 

 in 1916, the creosoted pile construction was considerably curtailed, and 

 pre-cast concrete pile construction somewhat extended. Pier 35 was 

 constructed in 1915 and Piers 3, 29, 31 and 33 in the period from 1916 

 to 1918. In these piers concrete piles up to 100 ft. in length have been 

 satisfactorily handled and driven. This construction together with the 

 concrete cylinder construction has been periodically surveyed for de- 

 fects and deterioration. The later concrete pile structures show no 

 deterioration as yet, but the earlier bulkhead wharves are beginning 

 to show cracks due to the rusting of the reinforcing above the water 

 line- No deterioration has been discovered below the water line. 



Summary 



The following types of substructure support have given satisfactory 

 service and may be considered reliable when properly designed and 

 constructed: 



1. Concrete piers and cylinders laid in open coffer dams; 



2. Steel cylinder shells filled with concrete; 



3. Single green piles encased in concrete; 



