Engineering Wonders of the World
Volume I

THE NEW YORK SUBWAY. 345 The Trouble with Buried Pipes. etc. Many of these must be shifted, but with- out interrupting their service. They cannot simply be removed, and later on restored, but must be supported over the trench most carefully and protected against the slightest settlement. This makes the whole work very slow, and very costly. How much extra cost was chargeable to this feature in the case of the New York Subway work is not known. No doubt it was a pro- digious item. Worse than the mere added cost, however, was that the work was delayed, and that the streets were so congested that the business interests of the city suffered very sensibly. These remarks apply to the sewers as well as to the water pipes. But the sewers intro- duced an important complication of their own. The Subway, running along the middle of Manhattan Island, cut right across the city’s sewer system. Sewer Diversion. What had previously been a single system, draining here to the Hudson, there to the East River, was converted into two separate systems draining west and east independently. To accomplish this con- version required a great amount of labour, both in planning and in execution. Sewers that were cut of? from their outlets had to be joined to other outlets. Many new outlets had to be built. Sewers draining toward the Subway had to be turned in the opposite direction. A very effective device used was to build an intercepting sewer along the side wall of the Subway, which received the discharge of the branch sewers, and turned off at a convenient point to an outfall. The sewer diversion work was carried on partly before the Subway building, partly in connection therewith. It was governed and made more difficult by the condition that no part of the sewer system should be put out of service at any time, a condition observed faithfully. Excavating and Building the Subway. The Subway was built in an open trench dug from the surface. Where necessary, car tracks, drive-ways, and walk-ways were carried along over the top of the trench on temporary supports. No part of the Subway where the shallow box type was em- ployed was built by tunnelling, the latter pro- cess being confined to those parts which are true rock tunnels—namely, under Murray Hill, Washington Heights, and the rock of th© north-west corner of Central Park. The reader is no doubt familiar with the methods used in rock tunnelling, so that we may confine our attention to the Subway work proper. To say that a trench was dug, the steel and concrete erected therein, and covered over again, is to summarize in a word a picturesque variety and complexity of method. The nature of the street traffic, the presence of car tracks, the nature of soil, of adjacent building foundations, etc., all demanded special adaptations at each different point of the route. Since we cannot describe all, for a broad view we may look at three contract- sections as exhibiting representative methods. In Elm Street, from City Hall north to Astor Place, there were no car tracks, no important traffic, and few lofty buildings. The work was therefore rela- tively simple (but see the view, ’* An ,^asy Fig. 4). Generally the con- Section, tractor opened half the width of the street, and dug out the earth down, to the desired bottom level. The sides of the trench, were usually held by sheet-piling, to protect the house foundations and prevent caving. Plank walks were bracketed out over the excava- tion, in place of the side-walks, where these had to be destroyed. When the trench was deep enough, a layer of concrete was deposited over the floor, and on this was laid a thick course of waterproof- ing of felt and asphalt. Over this came the real floor concrete, in which were formed also