Page:Popular Science Monthly Volume 88.djvu/734

 New York's Submarine Subway and How It Was Built

By Howard B. Gates

The author of this article is a Civil Engineer, who is connected with the Public Service Commission of New York city. His official duties were such that he was closely identified with the daring work that he so interestingly describes. Obviously, he writes from first-hand knowledge. — Editor.

��ATWENTY-story building literally grows out of the ground o^•er night; subways are built beneath our most congested streets and under rivers and we scarceh^ know they are there until they are ready for operation; our water supply is siphoned under rivers at great depths and runs through the very bowels of the earth in arteries hundreds of miles in length for our con- venient use at faucet and hydrant; bridges spring from the opposite banks of our rivers and meet in the center within a fraction of an inch and we talk with our friends across the ocean and continent with perfect ease and under- standing. Not only to the lay mind but to the technically trained as well, do these achievements become a source of wonder, the former accepting the result as sufficiently marvelous in itself, while the latter appreciating the underlying principles of science and laws of nature which contribute to their success, w'on- ders at the ingenuity of their applica- tion. One of the most recent examples of these marvels of engineering is the "submarine" subway or Harlem River tubes built beneath the Harlem River to form the connecting link between the Boroughs of Manhattan and the Bronx subway systems now nearing com- pletion.

The Harlem River at the point of this crossing is six hundred feet wide and varies in depth from twenty to twenty- six feet. In accordance with the require- ments of the Secretary of War, the top of the structure was fixed at a depth which placed it an average of seven feet below the river bottom and made the lowest point in the structure about fifty-seven feet below water. To start the con- struction at the bulkhead lines was not practicable; hence the tubes were pro-

��jected landwards, so that the total length of this special construction was one thousand and eighty feet.

The Four Tubes Floated Like Boats

Brief!}', the method consisted in as- sembling the steel shell or form of the four tubes, in sections about two hundred and twenty feet in length upon timber supports above the water. With the ends sealed or partially closed, a section was launched and floated as a boat. Towing it to and anchoring it above its designed location, its tubes were filled with water under positive and accessible controls and gradually lowered into a previously dredged and prepared trench. As each section was lowered in turn, it was attached to the end of the pre\'iousIy placed section and encased in concrete. When all of the sections had been lowered and properly encased, w^ith their ends closed by watertight walls or bulkheads, the water by which they had been sunk was pumped out, and a reinforced concrete lining was placed inside the steel shell to complete the structure.

The steel portion of the structure consists of four parallel tubes bolted together, with flat sides on their interior walls. Between the tubes are vertical diaphragm plates which are placed at intervals perpendicularly to the direction of the tracks and which extend to the rectangular limits of the structure.

Digging Trench for the Tubes in the Bottom of the River

The safe submerging of this light steel form and the temporary control and final location of it, comprise the most spec- tacular part of this great scheme. The trench into which the subway was to be located was formed by a "clam-shell"

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