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Fifty Years of Rapid Transit · James Blaine Walker Chapter XVIIIDecked Roadway Method Of Construction-Problems Met In The Work. In the contract for the construction of the Brooklyn extension of the subway there was a new provision, born of the experience in underground work gained in the building of the first sections, for the carrying on of operations without unduly disturbing the street surface or interfering with its traffic. In prosecuting the first contracts in streets where the subway was to run close to the surface, the contractor tore up the street pavement and began excavation just as he would for a gas main or a sewer, leaving the opening in the street a gaping wound in the surface until the steel structure was completed, when the backfill would be placed and the pavement restored. As large areas were badly obstructed for months at a time, this method of working seriously interfered with traffic and also greatly injured the business of the tradesmen having stores in the area affected by making access to their places so difficult as to discourage visitors. The extreme of this evil was felt in Forty-second street between Park Avenue and Broadway. Trade in the shops along the street fell off so that some merchants closed their places and others continued with reduced profits. Complaints poured in upon the Rapid Transit Commission, which wisely decided to prevent a repetition of such interference with normal conditions if its engineers could find a way. The engineers were equal to the emergency and devised what has since become known as the "decked roadway" method of subway construction. It was first tried in building the extension of the subway down Broadway from City Hall to South Ferry, and it was so successful that it was embodied in all future specifications. This method consists in replacing the ordinary street pavement with a temporary plank roadway strong enough to support the usual street traffic and excavating for the subway underneath it. As depth is attained in the excavation huge timbers properly braced are erected beneath the decking, which is kept in place till the steel frame of the subway is erected, when the temporary decking is removed, the backfill placed and the street pavement restored. The plan had two merits, first the business of merchants along the route and the ordinary street traffic were not interfered with, or if so only to a bearable degree, and, second, it kept the work of construction out of sight and thereby minimized interference from the outside. Since it was introduced in 1902 more than twenty miles of subway have been built according to the cut and cover method. This method of work involved another departure in the treatment of gas pipes encountered in the route of a subway. Covering the excavation produced a confined space between the bottom of the cut and the street decking, so it was feared that, should a gas pipe be injured so as to leak, the escaping gas would mix with the air in the cut and produce that highly explosive compound which when ignited works tremendous damage. To safeguard the work, therefore, the "by-passing" method was devised. That is, the service pipes were removed from the mains and carried around the cut in bypass pipes either laid close to the curb on the street surface or supported on trestles above the sidewalks. In either case the gas was removed from the cut and possible explosions were prevented. Only the engineers and contractors actually engaged in the work could tell of the thousand other problems encountered and solved during the construction of the subways. Almost every section had its own peculiar obstacles. For instance, in tunneling under the East River the contractor had to combat the water under the river bed while he was pushing the tubes across. The hydraulic shield and compressed air were invoked. The shield was pressed forward a few feet a day, the workmen, or "sand-hogs", excavating the material in front of it and installing the cast iron rings of the tubes under its protection, the water in the material above being driven out by compressed air introduced into the workings through pipes connected with compressors on the surface. Two of the most remarkable accidents ever recorded in compressed air work happened during the construction of the subway tunnels under the East River, and the second, although eleven years later, was almost a duplicate of the first. In each case a man was blown out of the tunnel by the force of the air, through the river bed and through the water to the surface and yet came out alive. The first accident occurred in 1905 during the construction of the Battery-Joralemon street tunnel of the first subway. As frequently happens, a "blow-out" took place. That is, the compressed air found a weak spot in the roof of the tunnel and began escaping. In such cases the usual treatment is for the men in the tunnel to heave bags of sand or clay into the vortex and thus stop the leak. On this occasion Dick Creedon, a workman employed by the contractor, attempted to plug the air hole with a bag of sand. The pressure of the air was so strong, however, that the "blow-out" sucked both bag and man into the vortex and forced them through thirty feet of sand and silt up into the waters of the river. On reaching the surface Creedon began swimming and was soon picked up by a boat, apparently none the worse for his marvelous experience. The "blow-out" was repaired by dumping tons of sand from scows immediately over the break. The second of these accidents occurred in 1916 in the Whitehall-Montague street tunnel of the Dual System subways, also under the East River. A "blow-out" occurred in the north tube a short distance out from the Brooklyn shore. The shield had just been shoved ahead for the placing behind it of another ring of the tunnel tube. Four workmen were about to place the top "breasting" board in its new position just ahead of the shield, when there was a rush of air and three of the four disappeared. They were sucked into the vortex and through twelve feet of sand to the river bottom. One of them, Marshall Mabey, shot up through the water and into the air on the top of a geyser which eye witnesses thought reached a height of forty feet above the surface. When he dropped back into the water he began swimming and was soon picked up by a boat sent out from the contractor's dock. He was practically unhurt. His companions were less fortunate. One was found unconscious in the river forty minutes after Mabey was rescued, but efforts to resuscitate him were unavailing. The body of the other was not recovered until the next day. It is supposed they were struck by some hard substance in their passage through the river bottom and either killed or made unconscious and then drowned. The break was repaired by placing a blanket of clay in the river bottom. All of Manhattan Island is underlain with rock, but it is closer to the surface in the northern part of the island than elsewhere, so that a subway running close to the surface of the streets passes through soft sand in the southern part and through solid rock in the northern part of the island. At low places, too, it must be built below water line. These varying conditions produced varying problems and taxed the ingenuity of the engineers to meet them. In the sand district the sides of the cut had to be buttressed with stout timber sheeting to prevent their falling in, while in the rocky section great stretches of tunnel were built with the walls of the cut unsupported except by the solidity of the rock itself. At many places, however, the rock is treacherous, and here great care had to be exercised. Whenever such rock was encountered the prudent contractor made assurance doubly sure by buttressing the rock walls with heavy timber braces. Natural mistakes were made on occasion in "diagnosing" the character of the rock, and in such cases gravity caused slides of varying dimensions. A notable instance was the slide in Park Avenue near Thirty-seventh street referred to in a previous chapter. Along Lafayette street near Canal street the subway passed through marshy ground, in places below the tide water level. Here pumps had to be used to keep the excavation clear of water while the work proceeded. It was also difficult to get a foundation of sufficient stability for the subway structure. Such conditions here and in other parts of the line made waterproofing necessary, and the first subway was liberally swathed in a coat of asphalt blankets to keep it dry. The waterproofing, it was found after the subway was opened, was impervious to air as well as water, with the result that it tended to keep the heated air, generated in the tubes by the friction of wheels and machinery, from escaping. In the later built subways this result was avoided by reducing the waterproofing. Perhaps the most difficult piece of work in the sand district during the construction of the first subway was the excavation in front of Trinity church in lower Broadway on the Brooklyn extension. This extension runs down Broadway from the City Hall to Bowling Green, where it turns eastward and runs under the East River to Brooklyn, two tracks, however, continuing down Broadway to the Battery. It was found that the foundation of the church spire was built on sand and extended only nine feet below the sidewalk level. As the subway was to be twenty-four feet down, it was feared the excavation in the street, which was to be only nine feet away from the spire foundation, would undermine it. To prevent this the work was done in three pockets. The central pocket was first excavated and in it was placed a mass of concrete for the floor and sidewall of the subway, the sand at the side being held up meanwhile by steel sheeting which was left in place after the work was finished. The pockets on either side of the central one were then treated in the same way in succession. After the work was done and the subway wall and floor were built in front of the church it was found that there had been no settlement of the spire. Another interesting piece of work on the first subway was the placing of the bridge over the Harlem ship canal near the old Kings Bridge, on the Broadway branch. The City already had a single deck bridge at the point, which was used for ordinary highway traffic. To accommodate the subway trains it was necessary to replace this bridge with a double-deck structure to carry ordinary traffic on the lower and the subway trains on the upper deck. The new steel bridge was assembled in sections on false work resting on barges anchored nearby. When it was ready to install, similar barges bearing cribbing were floated under the old bridge at low tide, and as the tide rose the old structure was lifted clear of its anchorages and floated away, when the new bridge was floated into the vacant place and lowered into position as the tide receded. The old bridge was floated down to 207th street, where it is now doing duty as a highway bridge. On several other occasions the rise and fall of the tide were utilized in this way to facilitate engineering operations.  Construction of First Subway. Lifting By Force of the Tide Old Bridge Over Harlem Ship Canal [Broadway Bridge]. Considering the magnitude of the work, the Dual System subway and elevated roads have been built with surprisingly little disturbance of normal conditions. Thanks to the cut and cover method of construction, traffic in the streets under which the new tunnels were built has gone on day by day with slight inconvenience to merchants along the routes. Of course, no such work could be done without inconveniencing somebody, but the inconvenience has been trifling compared to the trouble caused by the building of the first subway. The work was also remarkably free from accidents. A perfect record in this respect was spoiled by two of the worst accidents attending the Dual System construction, and singularly enough both occurred in the same month and within a few days of each other. Both were due to the collapse of the temporary street decking, but the causes were different. The first took place in the Seventh Avenue subway on September 22, 1915, and the second followed in the Broadway subway on September 25. The first was by far the worse. Just before eight o'clock in the morning, when rush hour traffic on the street surface was at its height, a blast was fired in the north heading of the excavation in Seventh Avenue, just south of Twenty-fifth street. From that point south to about Twenty-third street the avenue was decked over by planking supported by an elaborate system of timbering. As usual the two tracks of the surface car line, with their ties and concrete bed, were also supported in the same way so that trolley car operation might go on as usual. It is supposed that rocks dislodged by the blast were hurled against the nearest timbers supporting the decking and with such force as to knock them down. In falling they carried with them the supporting timbers to the south for a short distance, thus leaving a stretch of the street decking and heavy car track bed hanging in the air. The weight of the decking and car tracks on the over-hang proved too much for the remaining supports, which fell in quick succession and the whole street surface between a point south of Twenty-fifth street and a point south of Twenty-fourth street, or something over a block, fell to the bottom of the cut, a distance of thirty feet. A loaded trolley car was going north in Seventh Avenue at the time. As the tracks sank in front of it gravity forced it into the declivity and it slid to the bottom, where it landed a complete wreck. Some of the passengers were killed and others injured. Most of them got out or were helped out safe, but few escaped some slight injury. Police and firemen, with the contractor's men did heroic rescue work, but in spite of their efforts eight persons were killed. The injured were treated in an improvised hospital near by and later removed to homes or the hospitals. They numbered thirty or more. Within two weeks the contractors had the debris removed and the steel work of the new subway in place. It was found that the collapse of the decking had been stopped where the steel work ended, namely just north of Twenty-third street. When the pavement was replaced it rested on solid steel. Panic over this accident had scarcely subsided when the second collapse took place. This was on a section of the new subway in Broadway. On Saturday evening, September 25, at about, seven o'clock about seventy-five feet of the temporary street decking on the west side of Broadway just north of Thirty-eighth street sank into the excavation, falling about thirty feet. Fortunately there were few persons on the street at the time, and only one was killed. There was a taxicab standing at the curb when the pavement caved in, and it fell to the bottom of the cut, a distance of about twenty-five feet. The chauffeur had left it a moment before and was safe on the sidewalk when his machine went down. The timbering on the east side of the street held, so that only the decking on the western half fell in. The two trolley tracks hung in air and though they sagged badly they did not break and fall. It was only by the quick action of the motorman of a southbound car that a repetition of the trolley accident in Seventh Avenue was averted. He saw the street sink ahead of him, quickly applied the brakes and then reversed his power, sending the car backwards from the very brink of the yawning pit. The New York Railways Company rewarded him for his presence of mind, which no doubt saved the passengers from injury and possible death. This accident was caused by a slide of rock from the west side of the cut. The rock in this section is known by the engineers as treacherous, and wherever it looked suspicious extra precautions were taken to brace it. Here, however, there was a hidden seam which did not reveal itself until hundreds of tons of rock moved laterally into the cut, knocking down the nearest timbers supporting the street decking and causing the collapse. The timbering was exactly the same kind as that used in Seventh Avenue -- in fact the same contractors who had the Seventh Avenue work also had the Broadway contract. They used a combination of steel beams and timbers which was supposed to be particularly strong. Engineers of the Public Service Commission, however, held that any timbering would have given way if subjected to such a strain and did not find fault with the method used. The authorities took prompt action. The Public Service Commission opened an office at the scene and its engineers at once began the work of repairing the damage. The Mayor appointed a committee of engineers from the various City departments to investigate and this committee examined all contracts on which timbering was used to support the street decking and made recommendations for certain minor changes to strengthen the same. These were put into effect by the engineers of the Public Service Commission, which also appointed a board of three consulting engineers from other cities to study 'and report on the work. This board consisted of Edmund S. Davis, of Boston, Henry H. Quimby, of Philadelphia and D. O. Jackling, of San Francisco. Mr. Jackling could not serve and the work was done by Messrs. Davis and Quimby, who made a report in October, 1915, which in general approved the style of timbering used, made certain recommendations for improvement and suggested the employment of an engineer skilled in mining timber work to supervise all timbering. The Commission acted on the recommendations and added a mining engineer to its staff in the person of H. G. Moulton, who served throughout the remaining period of construction. More than two years before the decking accidents, namely in June 1913, a fatal slide of rock occurred in the Lexington Avenue subway work near 56th street. At this point the lower or express tunnel passes through rock, and as it was known to be treacherous the contractor installed timbering to support the roof and sides of the tunnel. One night a large portion of the roof gave reveal itself until hundreds of tons of rock moved laterally way and the enormous weight of many tons of rock thrown suddenly on the timbering caused it to fail. Eleven workmen were caught in the tunnel and buried by the cave-in. All were dead when taken out. There were several other accidents due to slides of rock, but none of great proportions. These caused some loss of life. The number of fatal accidents was small considering the magnitude of the work. In closing this chapter a word about the engineers of the Public Service Commission seems appropriate. At the height of construction the force numbered more than 2,000 employees. Its functions were many, but may be summarized under the following classifications: Studying traffic and population trend and laying out and surveying routes for rapid transit lines. Making general and detail plans for the construction of rapid transit roads and designs for elevated structures, subway and elevated stations. Reconstructing sewers interfered with by rapid transit lines and making plans therefor. Inspecting materials entering into rapid transit construction. Supervising actual construction of subways, elevated railroads and sewers, including passing on plans submitted by contractors or operating companies. The inspection of materials was thorough and extensive. Every bit of sand and cement used for the concrete work, every ton of steel placed in the structures, all bricks, lumber and mortar used in the work, all marble or other stone going into it, all tiling for stations, plumbing and station fittings of every description -- all had to pass the scrutiny of these engineers. The proper inspection of lumber, steel and cement involved the dispatching of competent men to the mills and other producing plants in distant states, but this was done and many such men maintained for years in out of town places. This saved the rejection of unfit materials after they had been delivered on the ground, resulting in economy for both the city and the contractor.
During the greater part of the Dual System work the engineering staff of the Commission was headed by the following men:
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