48 



tlons which seem to be required as a result of this year's work. All 

 changes of wording from that used last year are indicated by italic ft. 



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

 connected waters, and in places where their attack is severe will des 

 troy untreated piling in as short a time as six to eight months. In 

 ether places the untreated piling may last from two to four years. 



(2) The information secured indicates that it is reasonable to 

 expect a life of five to eight years from paint and batten protections 

 in sheltered waters, if the work is well done. If it is not well done, 

 or if the covering is damaged by careless handling, or if unprotected 

 wood is exposed by mud scour, this range of life cannot be expected. 



(3) The data so far in hand indicates that it is fair to r.n-jtecl 

 creosoted Douglas fir piling in Kan Francisco Bay to give a life of 15 

 to 20 years under present conditions. Certain piles are of authentic 

 record from the Oakland Long Wharf which were sound when removed 

 after a service of 29 years. Poor treatment, or damage to creosoted 

 piling by careless handling, rafting, storage or construction, will ma- 

 terially reduce the life which might otherwise be rendered by sucli 

 piling. 



(4) Most of the attack on creosoted piling by marine borers, 

 which the Committe has observed throughout this survey, appears to 

 have begun in spots where untreated wood has been exposed by dam- 

 age in handling the piles or placing the superstructure. It is urgently 

 recommended that improvements be made in the methods of handling 

 creosoted piles and building structures upon them, so that damage to 

 the surface of the piles may be reduced to a minimum. 



(5) Precast reinforced concrete piles and pile casings have not 

 been in use in San Francisco Bay a sufficient length of time to deter- 

 mine their ultimate life. A detailed examination of those structures 

 which have been in service for 10 years shows no evidence of deteriora- 

 tion below high water line, and they seem capable of a long further 

 life. The length of life to be expected from this type 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. 



(6) Reinforced concrete cylinders cast in open caissons have been 

 in use for twelve years. 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 

 with best modern concrete practice should constitute a type of construc- 

 tion only excelled for longevity by solid fill or mass concrete. 



(7) Cast in place concrete piles jackets may be expected to give 

 satisfactory results if properly constructed of suitable materials and 

 if proper regard is given toward exclusion of sea water from forms. 



