31 



pik's weru driven in each. FinalK' the>- were pumped dry ard filled with concrete, 

 and the pre-cast curved arch slabs then placed in position. (See p. 133.) 



In 1923 work was started on the Carciuinez Highway Bridge across Carquinez 

 Strait near Crockett. This structure, which was completed in May, 1927, consists of 

 two main spans 1 100 feet long, a central tower p'wr 150 feet wide, and a 500-foot anchor 

 span on either end, giving a total length for the main bridge structure of 3350 feet. 

 The substructure consists of concrete piers which cost about $2,000,000. These piers 

 are constructed in coffer dams carried down to rock, the two largest extending 140 

 feet below mean high water level. The total cost of the entire project was about 

 $8,000,000. 



The year 1924 was one of exceptionally low rainfall, which was even less than 

 in 1919, with the result that the salt water advanced further up the rivers than ever 

 before recorded. In doing so it carried the teredo infestation in the Carquinez Strait 

 beyond the region of heavy attack of 1919-1921) to points where unprotected piling 



Fig. 15. China Basin terminal diirint; construction, sliowing caissons after filling (workman whose 

 hands are blurred is standing in one) and pre-cast curved arch slabs in place. 



(Board of Slate Harbor Corns. Photo.) 



Still existed. \Vhar\-es which had previously been practically unmolested were severely 

 attacked. Even when the coming of the borers was carefully watched and plans made 

 accordingly for reconstruction, their progress was in some cases so rapid that, before 

 new materials could be assembled, structures were weakened to an extent such that 

 they were unable to withstand unusual impacts from vessels. Disasters coming thus 

 in spite of attention being given to the conditions illustrate the jeopardy involved in 

 wharves located in regions of marginal salinity between fresh and salt water. 



Another transbay structure, the Dumbarton Highway Bridge, has just been com- 

 pleted across the south end of the Bay, extending from San Mateo due east to the 

 opposite shore a short distance north of the present Southern Pacific Company rail- 

 road bridge. The new bridge includes eight 226-foot steel spans, one 228-foot steel 



