This paper will be limited to a consideration of the construction of thetunnels, the broader questions of design, etc., having already beenconsidered in papers by Brig.-Gen. Charles W. Raymond, M. Am. Soc. C.E., and Alfred Noble, Past-President, Am. Soc. C. E.
The location of the section of the work to be considered here is shownon Plate XIII of Mr. Noble's paper. There are two permanent shafts oneach side of the East River and four single cast-iron tube tunnels, eachabout 6,000 ft. long, and consisting of 3,900 ft. between shafts underthe river, and 2,000 ft. in Long Island City, mostly under the depot andpassenger yard of the Long Island Railroad. This tube-tunnel work wasnaturally a single job. The contract for its construction was let to S.Pearson and Son, Incorporated, ground being broken on May 17th, 1904.Five years later, to a day, the work was finished and received its finalinspection for acceptance by the Railroad Company.
The contract was of the profit-sharing type, and required an audit, bythe Railroad Company, of the contractor's books, and a careful system ofcost-keeping by the Company's engineers, so that it is possible toinclude in the following some of the unit costs of the work. These are[Pg 420]given in two parts: The first is called the unit labor cost, and is thecost of the labor in the tunnel directly chargeable to the thingconsidered. It does not include the labor of operating the plant, norwatchmen, yardmen, pipemen, and electricians. The second is called "topcharges," a common term, but meaning different things to differentcontractors and engineers. Here, it is made to include the cost of thecontractor's staff and roving laborers, such as pipemen, electricians,and yardmen, the cost of the plant and its operation, and allmiscellaneous expenses, but does not include any contractor's profit,nor cost of materials entering permanent work.
The contractor's plant is to be described in a paper by Henry Japp,[B]M. Am. Soc. C. E., and will not be dealt with here.
The contractors carried on their work from three different sites. Frompermanent shafts, located near the river in Manhattan, four shields weredriven eastward to about the middle of the river; and, from two similarshafts at the river front in Long Island City, four shields were drivenwestward to meet those from Manhattan. From a temporary shaft, near EastAvenue, Long Island City, the land section of about 2,000 ft. was drivento the river shafts.
The sinking of the temporary shaft at East Avenue was a fairly simplematter. Rough 6 by 12-in. sheet-piling, forming a rectangle, 127 by 34ft., braced across by heavy timbering, was driven about 28 ft. to rockas the excavation progressed. Below this, the shaft was sunk into rock,about 27 ft., without timbering. As soon as the shaft was down, onSeptember 30th, 1904, bottom headings were started westward in TunnelsA, B, and D. When these had been driven about half the distance tothe river shafts, soft ground was encountered. (See Station 59, PlateXIII.) As the ground carried considerable water