[62]

AMERICAN SOCIETY OF CIVIL ENGINEERS

INSTITUTED 1852


TRANSACTIONS


Paper No. 1152


THE NEW YORK TUNNEL EXTENSION OFTHE PENNSYLVANIA RAILROAD.

THE EAST RIVER DIVISION.

By Alfred Noble, Past-President, Am. Soc. C. E.

A general outline of the work included in this Division has beengiven by General C. W. Raymond, M. Am. Soc. C. E., in the first paperof the series. The few pages following are intended only as a note toconnect his paper with the more detailed descriptions of the executionof the work, which will be supplied by the Resident Engineers inimmediate charge.

Soon after the Company's project was made public, in the latterpart of 1901, borings were begun in the East River, and a few weekslater in Manhattan and Long Island City. A preliminary base linewas measured on the Manhattan side, and temporary transit stationswere established on buildings from which all borings in the river werelocated. The river borings were all wash-borings made from a pile-driverboat. After the results were plotted on the map, contour lineswere drawn to indicate the rock surface, and profiles along the tunnellines were plotted from the contours; as the borings were preliminaryto the final location of the tunnels, and in many cases at some distancefrom the tunnel lines, considerable divergence from the actual rocksurface was expected, and realized in a few places, yet on the wholethe agreement was very good. The borings revealed two depressionsor channels where the rock surface passed below the grade of theprojected tunnels, these depressions being separated by a rock reef[63]which extends down stream from Blackwell's Island. In 32d and 33dStreets in Manhattan, borings were made from the river to the stationsite at intervals of about 100 ft., wash-borings and core-borings alternating.In Long Island City, where the tunnel lines were to passdiagonally under the passenger station building and passenger yardof the Long Island Railroad and under streets and private property,the arrangement of borings was less regular, although the alternationof wash-borings and core-borings was carried out as far as practicable.After the final location of the work, additional borings were made,particularly on shaft sites and also along the approaches and in theSunnyside Yard, Long Island City.

A triangulation was carried across the river with a measured baseon each side. It was impossible to measure directly between theextremities of either base. The bases were measured with 100-ft.steel tapes, supported every 20 ft., stretched with a uniform pull, andfrequently compared with standardized tapes. On account of thecrowded condition of the streets during the hours of daylight andevening, most of the work was done between 10 P. M. and 5 A. M.Similar measurements were made in the streets along the tunnel lines.Angle readings were repeated many times, as is usual in such work.Fig. 1 shows the triangulation, the street measurements being omitted.

Levels were first transmitted across the river by simultaneous observationsof the river surface; then by several repetitions, acrossBlackwell's Island and the narrow channels on each side, where thelongest sights were about 1100 ft.; and, finally, by several lines throughthe tunnel of the East River Gas Company at 71st Street.

The franchise granted by the City of New York provided for thesale to the Railroad Company of the portions of 32d Street betweenSeventh and Eighth Avenues, and between Eighth and Ninth

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