LAYING WATER PIPES IN CONGESTED STREETS OF NEW YORK CITY
New York City, in consequence of its character as a still growing metropolis, has in almost every field a range of conditions from the simplest to the most complex. Thus, there are many sections of the city in which pipe-laying is no more difficult than in any small town or village. In lower Manhattan, however, any operation which involves the disturbing of the street surface and calls for underground construction, brings with it, in addition to the usual engineering problems, a multitude of incidental ones, which must also be handled and solved by the engineer as a part of the whole engineering work under his charge. In the narrow, curving streets of lower Manhattan, crowded normally to the limit with pedestrian and vehicular traffic, any constriction of the roadway by excavations in the street creates a traffic problem of first-rate importance. Allied therewith is the problem of arranging and carrying on the work so as to reduce to a minimum interference with normal business along the street. No less important is the safeguarding of the public against accident. Even minor accidents in an area of large crowds and high values have potentialities for heavy damage suits, against both the contractor and the city. However, all of these matters are but incidental to the work. The principal problem lies not above but below the street surfaces. Crowded as the roadway may seem, the space below it, in lower Manhattan, is still more congested. Many of the roadways downtown are less than twenty-five feet in width, some being as narrow as ten feet. In the space on each side of the sewer there are crowded, in irregular alignment, water mains, a multiplicity of gas mains, duct-banks, and distributor conduits for telephone, telegraph and electric power service, pneumatic tubes of the mail service and of the various telegraph companies, steam pipes encased in jackets increasing their diameter more than double, and a number of other minor pipes and conduits. To these there must be added, in some important cases, the superstructure and power conduits of the underground electric trolley, the Rapid Transit Subway, with its shallow covering, the column bases of the elevated railroad, and the tracks of the steam railroads and of the storage battery and horse-drawn street cars. The roadways, narrow as they are, are often further encroached upon by sidewalk vaults extending well beyond the curb line, and in some isolated cases beyond the middle of the street. In the broader avenues, also, the available space is occupied by trunk mains and heavy lines of conduits. In this crowded section of lower Manhattan, considered by many the most congested with sub-surface structures in the world, there were laid wiihin the last nine years one hundred and twenty-eight miles of new mains, comprising the Manhattan high-pressure fire system; a complete new network of water pipes. Investigations of sub-surface conditions in advance of construction work were at no time complete enough to determine even a general alignment for the new pipe in the street. When the first section of the Manhattan high-pressure system was planned, the Bureau of Sub-surface Structures, a recording bureau, had not been established in Manhattan. The alignment of the new mains was almost uniformly determined from an examination of test pits dug as the work progressed, together with such information as could be obtained from the incomplete records of the various departments and public service corporations, and from surface indications of existing sub-surface structures. Some special investigations were, however, made in advance of the work. These covered points known to be exceptionally difficult and complicated, such as street intersections along the route of the Rapid Transit Subway. The selection of locations for hydrants required a complete investigation and plotting of sidewalk vaults, which, in the business section of Manhattan, exist in front of almost every building. Detailed surveys of many of these vaults were required for the purpose of planning the construction of recesses to be built therein for the setting of hydrants. A most important item of the work was, thus, the alteration and reconstruction of existing structures, which was necessary to make room for the new mains. These alterations were both extensive and costly. In connection with a contract for fourteen miles of mains out of the total of one hundred and twenty-eight miles of maines mentioned, existing water mains were rearranged at two hundred and thirty-four locations; sewers and sewer structures were altered or reconstructed at one hundred and four points; fiftv-five waterproof recesses were built in existing sidewalk vaults to provide room for hydrants, and there were issued to public service corporations six hundred and forty-nine orders for alteration, removal or reconstruction of pipes, conduits or other structures owned by them. The cost of the last-named item to the companies was a considerable one. The service of the public service corporations in many sections would not bear lengthy interruption without great inconvenience, and often monetary loss to their consumers. Compelling quick action by the companies and assuring co-operation with the city and its contractors was often difficult. Yet there were many instances, such as the intersection of Frankfort and William streets, where, in accordance with special arrangements, five public service corporations removed their structures, which were badly intertwined, and replaced them again on the same day, a holiday, after the City’s contractor laid the new water mains across the intersection. At many points unusual construction had to be resorted to, or special provisions made to carry on the work. At many street intersections existing pipe formed such a complicated network that the entire intersection had to be tunnelled, in some cases for a distance of one hundred feet, and pipe dragged in. Where this occurred, the net work of piping formed an excellent roof for the tunnel. In digging the trenches, many interesting objects were uncovered. Old wooden water pipe of the early part of last century was very common. Much of it was in a good state of preservation. The wrought-iron bands at the bell ends were of especial interest. Wrought iron wedge gates in these pipes were more rare. A bronze driven tap with a piece of lead pipe attached was found in one of these wooden pipes. Cannon balls, and coins of the revolutionary and colonial periods were excavated in the streets near the south end of the island. At a number of points skulls and other human bones were plentiful. A broken coffin in Washington Square contained, among other things, a fine red wig, and close thereto a pair of old brass knuckles were found. On Elizabeth Street, under the sidewalk, at a point where hundreds of people pass every day, there existed an empty brick well 28 feet deep, covered over by only a badly broken piece of bluestone flagging. In Beekman Street, a fiveway casting with four 6-inch and one 10-inch branches formed a part of the old water main in the street. A number of structures, privately owned, occupying the street without franchise, were uncovered. Among them was a small tunnel across the entire width of the street, built to transmit power from one building to another opposite. In a number of downtown streets abandoned wrought-iron mains of an old steam distribution system were removed to make room for the new mains. On Front Street, for a distance of about two blocks, the trench pictured the history of the water main system for the last entury. In this trench there were exposed the old wooden water pipe, an abandoned 6-inch water pipe laid early in the century, a 6-inch water pipe laid in 1888. and a 12-inch water pipe laid in 1904. The removal of the first three made room for the new high-pressure main. That adverse conditions and the many difficulties encountered had little effect upon the quality of the resulting work, which was safeguarded by exacting specification provisions, is best shown by the results of the hydrostatic tests to which these one hundred and twenty-eight miles of mains were subjected after installation. The maximum rate of leakage allowed was four gallons per linear foot of pipe joint per twenty-four hours under a pressure of four hundred and fifty pounds maintained for twenty minutes. In the most difficult district covered the average recorded leakage on fourteen miles of mains was only 1.7 gallons per foot of pipe joint per twenty-four hours.
Assistant Engineer, Department of Water Supply, Gas & Electricity, New York City. Abstract of paper New England Water Works Association Convention. New York, Sept. 7-9, 1015.