Under-River Tunnel Headings Meet (1916)
Public Service Record · Vol. III, No. 12, December 1916.
Under River Tunnel Headings Meet.
The headings of the north tube of the Old Slip-Clark Street tunnel under the East River were "holed through" on November 28, providing an early Thanksgiving celebration for the "sand hogs" and other workers, the contractors and the Commission's engineers. The last blast, marking the official "holing through" ceremonies, was fired at 12:15 P. M. by Mr. George H. Flinn, president of the Flinn-O'Rourke Co., Inc., contractors for the tunnel.
A preliminary blast had been set off some two hours before, opening a hole in the intervening rock large enough for a man to crawl through, which some of the "sand hogs" did immediately after the smoke and gases from the blast had been cleared out of the tunnel. On the previous evening a drill had been sent through from one heading to the other, establishing that the two headings had met in almost perfect fashion, being less than one inch off line. This fact provided additional cause for celebration on the part of everyone connected with the tunnel work.
Met in Rock. The meeting was in solid rock as shown by one of the accompanying illustrations. The last 350 feet of the north tube were pierced through this rock, which is an under-river continuation southward of the hard ledge of Fordham gneiss which appears above the surface at Blackwell's Island and in Man-o'-War Reef. The headings of the south tube are proceeding to a meeting in the same rock and are due to be joined some time during the current months, possibly by the time this issue of the Record is off the press. The latter headings, however, will probably meet in a cross heading, driven from the north tube, which will eventually provide space for a pump chamber between the two tubes. In this pump chamber will be installed powerful pumps for the purpose of keeping the tunnel free from water. It is not expected that there will be any considerable amount of seepage through the cast-iron rings which form the tunnel or through its concrete lining. There is always the chance, however, that a broken water main or sewer on either land side may flood the sub-aqueous structure.
The last blast was fired in the presence of a gathering collected at the shaft house at Old Slip and Front Street, Manhattan. In this gathering were Commissioner Travis H. Whitney, Mr. Flinn, Major John F. O'Rourke, vice-president and chief engineer of the Flinn-O'Rourke Company, Inc.; Michael J. Quinn, general superintendent, and LeRoy Tallman, superintendent of that company; Clifford M. Holland, Tunnel Engineer of the Public Service Commission, together with other representatives of the Commission, the contracting company and a good-sited delegation of the "sand hogs" and other workers. The blast was fired from an electric switch on the side of the shaft house. One of the illustrations depicts Mr. Flinn in the act of "shooting" the blast.
Speeches Follow Blast. Following the setting off of the blast there were applause and cheering from the gathering. Brief speeches were made by Mr. Flinn and Commissioner Whitney. Then those of the party who desired descended the shaft and, headed by Major O'Rourke, walked through from the Manhattan side to the Brooklyn side. The trip consumed the greater part of an hour.
The holing through occurred almost at the center of the river. After a short examination of the effect of the last blast the party proceeded upon its way. Meanwhile, in keeping with tunnel construction precedent, the workers were holding their own celebration outside the shaft, being regaled with a bounteous "spread" provided by the contractors.
The Old Slip-Clark Street tubes form one of the four new East River tunnels under construction by the Commission and were driven by the shield method. As every employee of the Commission knows, the four tubes of the new Harlem River tunnel were not constructed by the shield plan, being built elsewhere and later placed in position in the river.
Minimum of Casualties. While the Old Slip-Clark Street work has not established a world-wide record for speed in sub-aqueous tunnel construction, it is claimed by the engineers that, as far as the north tube is concerned, it established a record for work underneath the East River. However, it does establish another and very important record, which many persons would doubtless hold to be much more important than the question of speed in construction, namely, that the work has been carried on with a minimum of fatalities and even of casualties. There has occurred on this work but one fatality from the dreaded caisson disease or "bends" as it is commonly termed in the tunnel building trade. Dr. Edward Levy of the Commission's staff, Dr. C. C. Emery of the contractors' force, and the engineers, as well, hold that this one fatal case of "bends" might have been saved, had the unfortunate victim notified the physicians and nurses of his illness. Before his plight was discovered, however, the man was unconscious and the disease had made such rapid progress that all efforts to save him were unavailing.
This highly creditable result was brought about by the adoption of rules for the conduct of the work and for the purpose of guiding the men along lines which would be most likely to prevent accidents and illnesses common to this kind of work. These rules were the result of scientific studies based somewhat upon the experience gained in building the Battery tunnel of the First Subway and of the other under-river tubes which were going forward at about the same time and others since built. While the casualty statistics of other tunnel work are not available it is said that generally the hazards have been accepted as high and that accidents have been common and cases of "bends" numerous. But one fatality among approximately 250 cases of "bends" treated seems to speak well for the care exercised over the workers.
Short Working Shifts. There have averaged five hundred men working in the four headings of the Old Slip-Clark Street tunnel. At one time the digging was being carried on under thirty-seven pounds air pressure, which was the maximum reached. The maximum allowed is only fifty pounds to the square inch. When the pressure was at its highest an average of more than a thousand men were employed, daily, owing to the short shifts permitted by law for caisson workers. At this period of the work the men were employed only one and one half hours at a stretch, entering the tunnels twice daily for an aggregate of three hours. The air pressure at the time of "holing through" had been reduced to eighteen pounds and will be continuously reduced as the tunnel is caulked and made water tight, so that normal pressure will have been reached by the time the tunnel is ready for its concrete lining.
Maximum progress made on the tube just opened was thirty-three feet per day and the monthly maximum 343 feet. Average progress per day was 4.9 feet. Some of the engineering problems met with were recently outlined in the Record by Mr. Holland.
The Old Slip-Clark Street tunnel is for operation by the Interborough under Contract No.3, and will carry the trains of the Park Place, Beekman and William Street subway to and from Brooklyn. Officially it is known as Route 48, Section 3, and extends from Old Slip and Water Street, Manhattan, under the East River through Clark Street to Fulton Street, Brooklyn.
Location of Shafts. Shafts are located at Old Slip and Front Street, Manhattan, and on Furman Street at the foot of Clark Street, Brooklyn. The section has a total length of 5,900 feet while the distance between the shafts is 3,800 feet. There is considerable shield driven tunnel work on the Brooklyn side, and, in addition, there will be a station at Henry Street, Brooklyn. Bids for this tunnel were received by the Commission on May 22, 1914. The contract was delivered on August 6, to Booth & Flinn, Ltd., and to the O'Rourke Engineering and Construction Company and later assigned to the Flinn-O'Rourke Co., Inc. The contract price was $6,469,916.25.
The tunnel is seventeen feet six inches in diameter and consists of two single track tubes. At greatest depth the bottom of the tunnel is eighty-eight feet below the surface of the river.