Pneumatic Caissons and the Manhattan Bridge

Discussion in 'Science and Technology' started by PoliticalChic, Mar 21, 2011.

  1. PoliticalChic
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    PoliticalChic Diamond Member

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    I’ve traversed the Manhattan Bridge countless times, but not until I found this explanation in Jed Rubenfeld’s novel “The Interpretation of Murder” did I envision how it was constructed.

    I ‘ll bet you’ll find it as engrossing, too…

    "The Manhattan Bridge, nearing completion in the summer of 1909, was the last of the three great suspension bridges built across the East River to connect the island of Manhattan with what had been, until 1898, the City of Brooklyn. As the longest single spans in existence, when constructed, were extolled by ‘Scientific American’ as the greatest engineering feats the world had ever known. Together with the invention of spun-steel cable, one particular technological innovation made tem possible: the ingenious conceit of the pneumatic caisson.

    The problem to which the caisson responded was this. The massive support towers for the bridge, necessary to hold up the massive suspension cables, had to rest on foundations built underwater, almost a hundred feet beneath the surface. These foundations could not be laid directly on the soft riverbed. Instead, layer upon layer of sand, silt, shale, clay, and boulder had to be dredged, broken, and sometimes dynamited until one reached bedrock. To perform such excavation underwater was universally regarded as impossible- until the idea of the pneumatic caisson was hit upon.

    The caisson was basically an enormous wooden box. The Manhattan Bridge caisson, on the New York City side, had an area of seventeen thousand square feet. Its walls were made from countless planks of yellow pine lumber, bolted together to a thickness of over twenty feet and caulked with a million barrels of oakum, hot pitch, and varnish. The lower three feet had been reinforced with boiler plate, inside and out. The weight of the whole: over sixty million pounds.

    A caisson had a ceiling but no man-made floor. Its floor was the riverbed itself. In essence, the pneumatic caisson was the largest diving bell ever built.

    In 1907, The Manhattan Bridge caisson was sunk to the river bottom, water filling its internal compartments. On land, enormous steam engines were fired up, which, running day and night, pumped air through iron pipes down into the great box. The forced air, building up enormous pressure, drove out all the water through boreholes drilled in the caisson’s walls. An elevator shaft connected the caisson to a apier. Men would take this elevator down into the caisson, where they could breathe the pumped, compressed air. There they had direct access to the riverbed and hence were able to perform the underwater construction previously considered impossible: hammering the rock, shoveling the mud, dynamiting the boulders, laying the concrete. Debris was discharged through ingeniously devised compartments, called windows, although on could not see through them. Three hundred men could work in the caisson at one time."

     
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  2. FuelRod
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    FuelRod Gold Member

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    The production and engineering feats of the early part of the 20th century never cease to amaze me. With the equipment that was available and what was accomplished? It's truly astounding.
    The mentality of today's society with that type of technology, we'd still be in mudhuts and covered wagons.
     
  3. PoliticalChic
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    PoliticalChic Diamond Member

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    A part of it is the attitude of societies toward learning, in large measure the result of the system of education in effect. I always liked this idea, from Simon Winchester.

    On Wednesday, June 6, 1928 the Oxford English Dictionary was completed. In "The Meaning of Everything," Simon Winchester discusses the English of the time as follows:

    “The English establishment of the day might be rightly derided at this remove as having been class-ridden and imperialist, bombastic and blimpish, racist and insouciant- but it was marked undeniably also by a sweeping erudition and confidence, and it was peopled by men and women who felt they were able to know all, to understand much, and in consequence to radiate the wisdom of deep learning.”
     
  4. Mr. H.
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    Mr. H. Diamond Member

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  5. rightwinger
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    rightwinger Paid Messageboard Poster Gold Supporting Member Supporting Member

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    Didn't a lot of the workers die of the bends?
     
  6. PoliticalChic
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    PoliticalChic Diamond Member

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    Astute point.

    Yes.

    And as a result, a 'book' was used on the work site, detailing how long the ascent should be staged, and how much time at each stage, depending on the time the worker had spent below.
    The elevator would remain at these stages, and were warned not to hold air in their lungs.

    Interesting, if one were only below for 10-15 minutes, no delay was necessary.
     

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