Launching a Bridge-Pier Caisson 



The caisson was built on a scow, on which it was towed 

 to position and from which it slid into the water 



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The caisson ready to be 

 towed out to its final 

 resting place as a sup- 

 port for one of the con- 

 crete piers of the bridge 



/%N interesting en- 

 r\ gineering feat was 

 performed recent- 

 ly at Manila, P. I., 

 when a timber caisson 

 for one of the concrete 

 piers of the Jones bridge 

 was launched in half 

 an hour. 



The caisson was built on a scow which 

 could be tilted so the caisson could slide 

 off into the water and be towed to its loca- 

 tion where it was to be sunk and the con- 

 crete pier built inside of it. The caisson 

 was 100 feet long, 35 feet wide and 36 

 feet high, longer and wider than an ordi- 

 nary city house. Three feet above the 



The scow was divided by a bulk- 

 head so that water could be ad- 

 mitted into one side to make the 

 scow list as the caisson slid off 



The only lines neces- 

 sary were those to keep 

 the caisson from float- 

 ing down-stream and 

 the towing lines 



lower edge of the caisson 

 was a 4-inch calked plank 

 floor supported by in- 

 verted timber trusses, 

 which in turn rested on 

 timber sills bolted to the 

 upper edge of the con- 

 crete walls. The floor 

 and trusses were designed 

 to withstand water pressure during flota- 

 tion. When all was ready, the valves on 

 the midstream side of the scow were 

 opened. When the caisson began to slide, 

 the scow was pushed from underneath 

 the structure. It was manned at once 

 and sunk by opening valves in the eight 

 compartments into which it was divided. 



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|— Tfir 



i. 



Twenty-three minutes after opening the 

 valves, the list was fifteen degree? 

 and the caisson slid into the water 



Due to the low center of gravity the cais- 

 son righted itself quickly and finally rested 

 on an even keel in eight feet of water 



89 



