152 



with best modern concrete practice should constitute a type of construction excelled 

 for longevity only by solid fill or mass concrete. 



(9) The selection of a type of piling or pile protection for a given structure must 

 be made upon the basis of cost and permanence of the materials under consideration, 

 the character of the structure and the probable need for future alterations to meet the 

 changing requirements of commerce. When a comparatively short increase over the 

 life of untreated wooden piling is sufficient, the surface protections will often be found 

 economical in waters not exposed to severe storm action; if a moderately long physical 

 life approximating the average economic life of marine structures in this harbor is 

 desired, a good creosote treatment will provide it at the lowest annual cost, so far as 

 present knowledge goes; where conditions warrant building for the greatest per- 

 manence, with less regard for first cost, concrete construction has shown a high value 

 in this harbor. For the protection from further damage of wooden piles already in 

 place and showing attack by borers, not yet severe enough to require condemnation, 

 the concrete casing, pre-cast or poured in place, is the only means of salvage found by 

 the Committee. 



Fig. 56. Piling treated by Muraii proct-ss, exposed 2 years at Georgia St. Wharf, Vallejo. Note 

 bulging and broken battens. (5. P. Co. Photo.) 



