established all over the United States by the United States Coast Survey, the United States Geological Survey and the United States Engineers, and all are referred to mean sea level at Sandy Hook as the Standard Datum of the country, there does not seem to be any good reason why the great City of New York should not adopt the same datum plane for all its surveys.

Not alone the United States Government, but almost every civilized country makes use of mean sea level as the zero of its determinations of elevations. This datum possesses, moreover, other advantages in addition to that of universality. As an origin of measurement it is superior to mean half-tide and, as has been shown in the foregoing discussion, affords a plane of reference not subject to changes due to the lapse of time. A large number of benches have now been established with elevations referenced to mean sea level and are available for the use of all whose work depends in any way on elevation. The time appears to be opportune for terminating an obviously absurd state of affairs under which the city, a single administrative unit, continues to perpetuate numerous unscientific and conflicting datum planes. inherited from its formerly unrelated constituent parts. It is to be hoped that in this not unimportant particular New York City will, in the near future, range itself on the side of progress and adopt a datum plane not merely universal as respects its own territory, but scientific in its origin and in harmony with the best practice throughout the civilized world.

BROOKLYN ENGINEERS' CLUB

No. 122

NEW YORK SUBWAYS-EXCAVATION AND CONCRETE.

BY HENRY L. OESTREICH, MEM. B. E. C.

Presented February 12, 1914.

The Tidewater Building Company and Thos. B. Bryson had the contract for building the section of four-track subway, known as Section 11-A-3, extending from Tenth Street to Twentyseventh Street, a length of 4,800 feet. Contract price about $2,000,000. (Figure 122 - 1.)

All the excavation of this section, except 178 feet at the south end, was above mean high water. This section, like the one north of it, is at the base of a large watershed. The building of the east longitudinal sewers to take care of this water was therefore the first work. Actual excavation was begun December 20, 1909. Water and gas mains and other subsurface structures were removed from under the roadway of Fourth Avenue and the water mains were relaid in permanent locations in the proposed pipe galleries under the sidewalks. (Figure 122-2.)

To meet the requirements of the specifications two 121⁄2-foot temporary roadways were built for the whole length of the contract. These roadways were supported by wooden piles driven just outside of the line of the subway, spaced about 7 feet apart. The driving of these piles was done by the subway contractor with equipment hired from Barth S. Cronin Co. A 2-inch pipe was. driven ahead of each pile, using the same as a jet with a water pressure of about 50-100 pounds per square inch. After sinking about 20 feet, the jet-pipe was withdrawn, and the spruce piles were driven by means of a drop-hammer. They drove hard and many were later found to be broomed and telescoped. The piles were capped with 12-inch by 12-inch longitudinal pieces. On these rested 3-inch by 10-inch floor beams, 12 inches c:c. The floor consisted of a 3-inch yellow pine longitudinally and 3-inch beach crossing it as a wearing surface. This made a good, rigid roadway. An 8-foot fence at the edge of the roadway kept the horses from shying at the sight of the steam shovel and trains

in the cut, but unfortunately did not keep the small boys from throwing stones at the men working below. Every contractor knew that his own work was the best, but each contractor would swear that the boys in the neighborhood were the worst.

Since the steam shovel had to have a clear field to work in, the Edison ducts were broken out and the cables were hung on the 8-foot fence at the edge of the temporary roadway. A temporary 12-inch wrought iron pipe was laid under each sidewalk as a by-pass for the gas. At a few points pressure gas mains crossing Fourth Avenue were maintained by suspending them about 20 feet above the street by means of steel cables passing over masts on each side of the avenue.

On April 23, 1910, a 70-ton steam shovel with a 21⁄2 cubic yard dipper began work of excavation for the tunnel trench near Fifteenth Street (Figure 122-3 and Figure 122-4). To work the shovel one 8-hour shift there were required one foreman, one engineer, one craneman, ten laborers, four dinkeys and their engineers and 35 dump cars.

The shovel loaded the excavated material into 6-car trains of side-dumping pattern, holding about 4 cubic yards, hauled by 20-ton locomotives on a 3-foot gauge track. These trains passed from the side of the shovel out of the cut and traveled over the surface of Nineteenth Street to the contractor's yard at Gowanus Canal, where the material was dumped into scows and hauled to sea. The average haul to the Nineteenth Street dump was about half a mile. To avoid a runaway, due to accidental parting of the train in the middle, the locomotive was always kept on the down-hill side while on Nineteenth Street. The material excavated was loam and sand, gravel and some boulders (Figure 122-5). As was expected from watching the driving of the piles, the sides of the cut stood at a steep slope, requiring bracing and sheeting for only the lower half of the trench. The steam shovel worked two 8-hour shifts from April 23, 1910, to October 17, 1910, and one 8-hour shift until November 28, 1910. The shovel was then sold by the contractor for about $2,000 less than he paid for it, after having taken out about 242,000 cubic yards or 80 per cent. of the total excavation. The record day was August 2, 1910, when 4,000 cubic yards were taken out in two shifts of eight hours each. The week ending August 6, 1910, gave a record of 16,607 cubic yards, and they "would have done better if August 3 and 4 had not been rainy afternoons.”