Scientific American
12 November 1870
BETWEEN NEW YORK AND BROOKLYN
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...ITS PRESENT CONDITION... SOME ACCOUNT OF THE METHOD OF PROCEDURE We give herewith some engravings, showing various operations in the interior of the caisson at the Brooklyn terminus of the East River Bridge. This caisson is now only nine feet from its permanent bed, and the sinking is progressing at the rate of about one foot per week. The interior is lighted by the oxyhydrogen light, or rather a light produced by the burning of jets of oxygen, and common illuminating gas in contact with pencils of magnesia. Col. W. A. Roebling, the Engineer-in-Chief, informs us that these lights are almost absolutely essential to the rapid progress of the work, as they emit neither smoke nor odor and the air in the caisson is in consequence kept pure and wholesome. Three gangs of men - one hundred in each gang - and working eight hours each, are employed in the caisson, and the work proceeds without intermission night and day. It will be just one year on the 1st of January since the first ground was broken, and the rapidity with which the work has proceeded is evidence that it is conducted by a man who is fully competent to conduct this greatest engineering feat of modem times to a successful issue. It is hoped that before the extreme cold weather of mid winter the caisson win have been sunk as low as necessary. The caisson for the New York side is about one third done, and will be placed in position as soon as possible after completion. Our readers have already been made acquainted with the nature and use of the caisson. It may be said to be a huge diving-bell from which the water is excluded by forcing into it air from a series of powerful air pumps worked by steam. In this bell the men work in safety and comfort, excavating and blasting, and sending the broken and excavated material to the surface in a manner hereinafter to be described.  1. ENTRANCE TO THE AIRLOCK OF THE CAISSON 2. MOUTH OF THE CAISSON AIRLOCK Fig. 1 represents the entrance to the caisson. It is a hollow iron shaft, having a vestibule or chamber communicating with the external air through a hatchway. Upon entering this vestibule the hatchway is closed, and the air from the caisson admitted through a hatchway in the floor of the chamber. To those unaccustomed to it, the pressure produces a series of very disagreeable sensations, which diminish somewhat after remaining a short time within the caisson. The lower end of the entrance shaft or "air lock," as it is technicany called, is shown in Fig. 2. The caisson in its descent requires the removal of a hard yellow clay in which are embedded large boulders which have to be broken up by blasting. Fig. 3 shows the workmen drilling one of these boulders situated under the shoe of the caisson. It not unfrequently happens that these boulders project some distance beyond the external edge of the shoe, and necessitate the passing out of workmen beyond this edge. This is done without danger, as the superimposed earth is of sufficient thickness to sustain the water resting upon it, the shoe of the caisson being now a considerable depth below the bottom of the river.  3. DOOR THROUGH PARTITION, SHOWING DIFFERENT APARTMENT IN THE CAISSON 4. DRILLING THE ROCK AT THE SHOE OF THE CAISSON Our readers have been informed in previous articles, and, in the report of Col. Roebling published in this journal in our issue of July 2, 1870, that the interior of the caisson is separated by partitions into chambers, from either of which the water may be expelled independently of the others. Fig. 4 represents the interior of one of these chambers and the door which leads from it to an adjoining chamber of similar character. Through these doors the broken stone and soil are wheeled over plank-ways to the mouth of the watershaft at the bottom, shown in Fig. 5.  5. FEEDING THE POCKET OF THE WATER SHAFT IN THE CAISSON 6. WORKMENT SAWING TIMBERS FOR WEDGES This shaft extends to and below the general level of the bottom, a hole or "pocket " being dug out around and beneath it, and filled with water by hose. The pressure of air in the caisson causes the water to rise in the shaft, and the dredges are lowered through this water to clutch and scoop up the material to be removed, the clay, broken stone, and earth being dumped from the barrows into the pocket, and shoved under the foot of the water shaft by men with iron bars, as shown in Fig. 5. The caisson with its load of masonry, now weighing upwards of 20,000 tons, does not rest upon its shoe, and is only in part sustained by its floating power. The greater portion of the weight is sustained by timber frames, the uprights of which are sustained by blocks and wedges. To lower the caisson the wedges are driven partly out, and as the impact of the enormous weight in its descent often crushes the blocks and wedges, it is necessary to supply their place by new ones. This necessitates the use of considerable timber, which is sawn by hand in the interior of the caissn, as shown in Fig. 6. The interior of the structure, with its manifold operations, all progressing with the utmost regularity, the whole illuminated by the brilliant oxyhydrogen light, forms a scene which, once seen, will not soon be forgotten. |
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