25 



In 1909 the design for subsequent seawall construction was changed from the 

 loose rock type to include a core wall of mass concrete supported on piles. This was 

 done to provide a definite bearing for structures to l)e built on the wall, thus avoiding 

 the settlement which steadily continued in the loose rock type; the piling furthermore 

 added stability to the seawall and served to fix the rock in a more compact mass. 



CiTV B*5E El±0 



rSSsSfc*;-"'" ''"" •-Hi'"' 



Fig. 11. Cross section of seawall 



(Board of Stale Harbor Corns. Photo.) 



That same year an experiment was made with twelve hundred piles of untreated 

 Eucalyptus, for which high claims had been repeatedly made, to ascertain their 

 ability to withstand borer attack. The\' failed very rapidly and were removed in a 

 few years. 



In 1911 reinforced concrete piles were introduced in structures both in San Fran- 

 cisco and Oakland. This type has since been used successfulK- in numerous structures, 

 although insufficient time has elapsed to judge its ultimate life. 



In 1912-1913 a biological survey of the Bay was made by the United States 

 Bureau of Fisheries, cooperating with the University of California. It is of interest 

 that no Teredo navalis was found in the survey, indicating either that it had not 

 arrived in the Bay or was present only in s^all, isolated numbers. 



In 1914 the Harbor Board reported that the three-pile concrete cylinders had 

 for the most part proved "costly failures." In six piers these cylinders had failed in 

 from seven to fifteen years. They had cost about three times as much as creosoted 

 piling without giving any longer life. Thus the latter type was once again reinstated 

 to the position it had formerly occupied. In the next two years six piers were repiled 

 and nine new piers constructed with creosoted piling. Meanwhile, hope for a solution 

 of the problem in the direction of concrete was transferred to reinforced concrete piles, 



