Page:EB1911 - Volume 27.djvu/420

Rh New York Tunnel Company. They carry subway trains. In one of the blow-outs of compressed air a Workman was blown through the gravel roof into the river above. He lived until the next day. Two other tubes of the same size built also through gneiss and gravel between 1905 and 1907 by the Degnon Contracting Company, with R. A. Shailer as the contractors engineer, go from 42nd Street to Long Island City. Four much larger tubes (see ng. 3) built in 1904 to 1909, for the Pennsylvania railroad, with Alfred Noble as chief engineer, S. Pearson & Son as contractors, and E. W. Moir as general manager, cross from 32nd and 33rd Streets to Long Island. The maximum average progress per day (one heading) for the best month's work was: rock, 4-1 ft.; rock and earth, 3-8 ft.; earth, with full sand face, 12-8 ft. The best methods of preventing blow-outs were found to consist of employing clay blankets (sometimes 2 5 ft. thick) on the river bed, which could be carried up to 20 ft. depth of water, and of filling the pores of the sand and gravel with blue lias lime or cement grout. The maximum air pressure was 38 lb per sq. in. In the case of sand face with poor leaky cover the usual practice was to make the air pressure equal to that of water from the surface down to about a quarter the distance below the top of the shield. The average amount of free air supplied per man per hour was approximately 2300 cub. ft. On the Hudson river side two tubes of the same size as those in the East river are for the Pennsylvania trains to New Jersey. Two tubes from Morton Street to New jersey, begun by Haskin, already referred to, are for subway trains, and so are the most southerly of all on the Hudson side, viz. the two from Cortlandt Street to under the Pennsylvania station in jersey City.

The two tubes from Morton Street were completed under the direction of Charles M. Jacobs, who was also chief engineer of the four other Hudson River tubes. The contractors for the Hudson tubes for the Pennsylvania road were the O'Rourke Contracting Company. Skilful treatment was required to overcome the difficulties on the New York side of the Hudson in all the tubes where the face excavation was partly in rock and partly in soft earth. Most of their length, however, was through silt, and in this the tunnelling was the easiest and most rapid that has ever been carried out in sub aqueous work, 50 lineal ft. per day being sometimes accomplished. A large proportion of the silt which under ordinary processes would be taken into the tunnel through the shield, carried to the shore and got rid of by expensive methods, was by the latter process merely displaced as the shield with nearly or quite closed diaphragm was pushed ahead.

The East Boston tunnel, the first important example of a shield-built monolithic concrete arch, from the Boston Subway to East Boston, is 1-4 m. long, 3400 ft. being under the harbour. One mile was excavated by tunnelling with roof shields about 29 ft. wide, through clay containing pockets of sand and gravel. The engineer was H. A. Carson, and the contractors the Boston Tunnel Construction Company and Patrick McGovern. Some 25 m. of waterworks brick-lined tunnels have been built since 1864, mostly in clay, under the Great Lakes, without the use of shields, though in the later ones compressed air was utilized. A large portion of the latest Cleveland tunnel, 9 ft. interior diameter, was built at the rate of 17 ft. per day at a cost of about $18 per ft. During this work three explosions of inflammable gases occurred, in which nineteen men were killed and others were injured. Later a fire at the shaft in the lake caused the death of ten men. Work was thereafter completed under the engineering direction of G. H. Benzenberg. Less serious accidents, principally explosions of marsh gas, occurred in many of the other tunnels. In one case (at Milwaukee under Benzenberg) drift material was penetrated, with large boulders and coarse afnd fine gravel, and without any sand or clay filling, apparently in direct communication with the lake bottom. At times the necessary air pressure was 42 lb per sq. in.-Subaqueous

Tunnels ma/ie by sinking Tubes, 'Caissons, &'c.—In 1845 De la Haeye, in England, doubtless having in mind the tedious and difficult work of the Thames tunnel, proposed to make tunnels under water by sinking large tubes on a previously prepared bed and connecting them together. Since then many inventors have proposed similar schemes. In 1866 Belgrand sank twin plate-iron pipes, 1 metre diameter and 156 metres long, under the Seine at Paris for a sewer siphon, and there have since been numerous examples of sunk cast-iron sub aqueous water-pipes. It is believed that the first tunnel of this class, large enough for men to move upright in, was by H. A. Carson, assisted by W. Blanchard and F. D. Smith, in 1893-1894, in the outer portion of Boston harbour, for the metropolitan sewer outlet. The later tubes were about 9 ft. exterior diameter, in sections each 52 ft. long, weighing about 210,000 lb, made of brick and concrete, with a skin of wood and water-tight bulkheads at each end. A trench was dredged in the harbour bed and saddles were accurately placed to support the tubes. The latter, made in cradles above water alongside a wharf, were lowered by long vertical screws moved by steam power, and were towed é to #2 m. to their final positions. After sufficient water had been admitted they were lowered to their saddles by travelling shears on temporary piles. 'The temporary joints between consecutive sections were made by rubber gaskets between flanges which were bolted together by divers. The later operations were back filling the trench over the pipes, and in each section pumping out the water, removing its bulkheads, and making good the masonry between consecutive bulkheads, this masonry being inside the flanges. T his work, about 1500 ft. in length, was done without contractors, by labourers and foremen under the immediate control of the engineers, and was found perfectly tight, straight and sound. cg

1'he double-track railroad tunnel at Detroit, made in 1906-IQOQ, under the direction of an advisory board consisting of W. J. Wilgus (chairman), H. A. Carson and W. S. Kinnear (the last-named being chief engineer), is 1% m. long, with a portion directly under the river of é m. The method used under the river (proposed by Wilgus) is an important variation on the Boston scheme. -A trench was dredged with a depth equal to the thickness of the tunnel below the river bed and about 70 ft. below the river surface, and grill ages were accurately placed in it to support the ends of thin steel tube-forms, inside of which concrete was to be moulded and outside of which deposited. These tubes, each about 23 ft. in diameter and 262' 5 ft. long, were in pairs (one tube for each track), and were connected sidewise and surrounded by thin steel diaphragms 12 ft. apart. Planking, to limit the concrete, was secured outside the diaphragms (see fig. 3). The forms were made tight, bulk headed at their ends, floated into place, -sunk by admitting water, set on the grill ages, and the ends of successive pairs connected together by bolts through rubber gaskets and fianges. The succeeding pair of tubes was not lowered until concrete had been deposited through the river around the tubes of the preceding pair. The following steps were to remove the water from one pair of tubes, mould inside a lining of concrete 20 in. thick, remove the contiguous bulkheads, and repeat again and again the processes described until, the sub aqueous tunnel was complete.

The New York Rapid Transit tunnel under Harlem river, built 1904-1905, has two tubes, each about 1 5 ft. diameter and 400 ft. long, with a surrounding shell of cast iron itself surrounded by concrete. The outside width of concrete is about 33 ft. Its top is 28 ft. below high' water and about 3 ft. below the bed of the river. D. D. McBean, the sub-contractor, dredged a trench in the river to within 7 or 8 ft. of the required depth. He then enclosed a space of the width of the tunnel from shore to mid-stream with 12-in. sheet piling, which was evenly cut off some 2 ft. above the determined outside top of the tunnel. On top of this piling he sank and tightly fitted a fiat temporary roof of timber 3 ft. thick in sections, and covered this 'with about 5 ft. of dredged mud. ~ Water was expelled from this sub aqueous chamber by compressed air, .after which 'the remaining earth was easily taken out, and the iron and concrete