151 



CONCLUSIONS BASED ON SERVICE RECORDS 

 (As of Year 1926) 



(1) Marine borers are very active in San Francisco Bay and connected waters, 

 and untreated piling will be destroyed in as short a time as six to eight months in 

 places wliere their attack is severe. In places where attack is less severe untreated 

 piling nia\' last from two to four years. 



(2) Copper sheathed piles ha\-e given very satisfactory service in locations where 

 damage from abrasion and theft can be minimized. Such piles carefulh' prepared 

 and handled fall into the class of best surface protections, when used under the con- 

 ditions indicated, but are easily damaged by either abrasion or theft. 



(3) The information secured indicates that it is reasonable to expect a life of tive to 

 ten years from paint and batten protections in more or less sheltered waters, if the 

 work is well done. If it is not well done, if the covering is damaged by careless 

 handling or by storm battering, or if unprotected wood is exposed by mud scour, this 

 range of life cannot be expected. 



(4) The data in hand indicate that creosoted Douglas fir piling in San Francisco 

 Bay has given a life of 15 to 20 years under past conditions and practice. Certain 

 piles are of authentic record from the Oakland Long Wharf which were sound when 

 removed after a service of 29 years. Some of these, redriven, are still in serviceable 

 use after 35 years. Poor treatment, or damage to creosoted piling by careless handling, 

 rafting, storage or construction, will materially reduce the life which might otherwise 

 be rendered by such piling. With improvement in these practices, which is already 

 in evidence, it is fair to expect an increase in life up to the maximum already of record. 



(5) Most of the attack on creosoted piling by marine borers, which the Committee 

 has observed throughout this survey, appears to have begun in spots where untreated 

 wood has been exposed by damage in handling the piles or placing the superstructure. 

 It is urgently recommended that methods of handling creosoted piles and building 

 structures upon them be universally adopted, by which damage to the surface of the 

 piles may be reduced to a minimimi. dratifying impro\ement in this respect has taken 

 p)lace during recent years. 



(6) Pre-cast reinforced concrete piles and pile casings have not been in use in 

 .San Francisco Ba>' a sufficient length of time to determine their ultimate life. A detailed 

 examination of pre-cast concrete pile jacket structures which ha\'e been in ser\-ice for 

 15 to 18 1,-ears shows no e\'idence of deterioration below high water line, and they seem 

 capable of a long further life. Gunite coated piles ha^"e given satisfactory service for 

 more than 12 years, with no serious deterioration. The length of life to be expected 

 from these types of construction is largely dependent upon the quality of materials 

 and workmanship and the skill and care with which they are employed, and any 

 laxity in these particulars will materially shorten the length of service which may 

 be secured. 



(7) Cast-in-place concrete pile jackets may be expected to give satisfactory 

 results if properly constructed of suitable materials and if proper regard is given to 

 exclusion of sea water from forms. The difficulties of this type of construction, how- 

 ever, are of such nature that the probability of securing a maximum length of life 

 is less than in the case of pre-cast concrete piles or pile casings. 



(8) Reinforced concrete cylinders cast in open caissons have been in use since 

 1910. Although the average life of many earlier cylinders has been considerably 

 shortened by construction defects, these cylinders with minor repairs still give promise 

 of a long period of service. Similar cylinders designed and constructed in accordance 



