. Engineering and Contracting. ier,or settling on inclined shores.—but very oftenwithout success, as the piers had become veryheavy on account of the masonry placed tokeep them above high water. Where thesemethods were unsuccessful in correcting theerrors in position the stone shaft was latershifted slightly on the large area of the con-crete foundation block, or the batter of thesides modified. As the caisson neared the bottom, gravel andboulders were often encountered of such sizethat the blow pipes could not handle this case a large airlock, known as theclay-hoist, was placed in pos
. Engineering and Contracting. ier,or settling on inclined shores.—but very oftenwithout success, as the piers had become veryheavy on account of the masonry placed tokeep them above high water. Where thesemethods were unsuccessful in correcting theerrors in position the stone shaft was latershifted slightly on the large area of the con-crete foundation block, or the batter of thesides modified. As the caisson neared the bottom, gravel andboulders were often encountered of such sizethat the blow pipes could not handle this case a large airlock, known as theclay-hoist, was placed in position on top ofthe material shaft and the material lockedthrough it. When all the debris had beencleaned from the bedrock, using the waterjet, a highly polished and hard crystallinelimestone was exposed. The bedrock in thebottom of all the piers was deeply corru-gated and waterworn. It was drilled severalfeet to ensure that it was not merely alayer or ledge overlying softer strata, andpreparations were then made for Fig. 1—Caisson for McKinley Bridge, St. Louis, Mo. of the caisson and its adjustment into exactposition, during sinking. When all was in readiness for the launch-ing, the timber work being only partiallyplaced to reduce the draft required, the plankswhich held back the skids were sawed, eightor ten teams of sawyers working in unison, sothat each skid might be released at the sameinstant. When but a fraction of an inch ofthe planks held back the caisson, jacks weretightened to increase the tension until theplanks parted and the caisson traveled withrapidly increasing velocity down the fastened to it before launching wereused to tow it to position, where each end inturn was lined into exact position by observ-ers placed at the baseline stations on shore. As soon as the caisson was secured in posi-tion, the contractors fleet was moved along-side. This consisted of a derrick barge, an-other containing cement storehouse and mixer,and the sand and
Size: 2218px × 1127px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, bookidengineeringcontr33chicuof
