34 



An examination by diver has verified last year's statement that the 

 Holmes piles of Pier 34, in contrast to the Holmes cylinders in other 

 piers, are in good condition and confirms the conclusion that satis- 

 factory results with this method depend largely on intelligence and 

 skill of execution which is difficult to obtain under working conditions. 

 Records of Black Patent pile repairs on the San Francisco Waterfront 

 indicate failures through neglect in penetrating the bottom at the mud 

 line- In the recent modification of this process, known as the Larsen 

 patent, as installed by Mr. Frank Camp at the California Wharf and 

 Warehouse, Port Costa, an attempt has been made to remedy this de- 

 fect by jetting the lower section into the mud bottom. In this partic- 

 ular structure 2259 piles were repaired and reinforced during the past 

 year and deducations with regard to durability cannot yet be made. 

 As shown in the table, 192, or 8.5% of the total, required patching or 

 repairing, either during construction or before acceptance of the job. 

 This job, however, illustrates one practical advantage of the method, in 

 that these extensive repairs were executed without the interruption of 

 a heavy grain warehouse business. (Plate 3, Fig. 2; Plate 4, Fig. 1.) 



In general it may be stated that uniformly dense and impervious 

 coatings of concrete extending from well below the mud line to above 

 the water line and reinforced sufficiently to resist blows and internal 

 stresses offer a highly satisfactory method of protecting untreated 

 piles. The service tests bear out theoretical contentions that coatings 

 of the high quality required are readily obtained in pre-cast work 

 and that under favorable conditions they may be obtained by skill 

 and intelligence in cast-in-place methods. 



Cast-in-place protections offer the only commercial method of re- 

 pairing defective piles and supports in place. Their value for tnis 

 purpose when applied between high and low tide is attested by the 

 numerous installations in all parts of the Bay. The durability of these 

 repair coatings below low water depends on the effectiveness with 

 which water, both sea water and excess mixing water, is excluded 

 from the concrete and a proper seal is made at the mud line. Nothing 

 .has developed during the year to alter last year's conclusions, that 

 such cast-in-place repairs are not certainly reliable for depths in excess 

 of fifteen feet. 



Creosoted Piling 



In adding the additional data brought to light during the present 

 year to the service records of creosoted piling in San Francisco Bay 

 presented in last year's report, occasion has been taken to segregate 

 the record of large structures according to years of installation of the 

 piling, instead of lumping them all in one record as was done last 

 year in the case of the Oakland Long Wharf. It is felt that such a pol- 

 icy will not only permit the determination of replacements by years, 

 and thus facilitate the pursuance of maintenance and depreciation 



