The distance between shafts is 700 feet. The cost was £287,000. This tunnel was not a financial success because of competition by a municipal ferry and its use, though interrupted, was resumed.
In 1891 the tunnel of the Ravenswood Gas Co. in New York city was started by Jacobs and Davies, engineers, crossing be neath the East River and Blackwell's island from between loth and 71st streets in Manhattan, to Ravenswood in Long Island city. It was expected to be a rock tunnel throughout and the section was to be 8 ft. 6 in. high and io ft. 6 in. wide, to provide room for two 3 ft. and one 4 ft. gas mains. Soft ground was encountered and great difficulty was found because of the depth and water pressure. Compressed air was adopted, the pressure at times reaching as high as 46 lb. per square inch. Eventually, it was necessary to line the soft ground sections with cast iron rings of 10 ft. 2 in. internal diameter. The work was completed in The notable Blackwall tunnel, under the Thames about 6 m. below London bridge (Sir Alexander Binnie, engineer, and S.
Pearson and Sons, contractors), was built in 1892-97, through clay and 400 ft. of water-saturated gravel. The tunnel is about 3,116 ft. long, the external diameter 27 f t. and the internal diameter 24 ft. 3 inches. The shield, 19 ft. 6 in. long, contained a bulkhead with movable shutters, as foreshadowed in Baker's proposed shield (fig. 2). There are a roadway 16 ft. wide for vehicles and two footwalks 3 ft. wide. The maximum grade is 2.78%.
Numerous tunnels of small diameter have been constructed by the use of shields under the Thames and Clyde for electric and cable ways, several for sewers in Melbourne and under the Seine at Paris for sewer siphons.
The Rotherhite tunnel, under the Thames, about 2.25 m. below London bridge, provides for a vehicular roadway 16 ft. wide and two footwalks 4 ft. 8 in. wide. It has a length of 4,863 ft. be tween portals, of which about 1,400 ft. are directly under the river. The exterior diameter of the tunnel is 3o ft. and the interior 27 feet. The maximum grade is 2.7%. It is constructed of cast iron rings and concrete lining, and a shield and compressed air were used. It was begun in 1904 and finished in 1908. Maurice Fitz maurice was the engineer of design and construction, and Price and Reeves the contractors. The top of the main tunnel exca vation in the middle of the river was only 7 ft. from the bed of the Thames, and a temporary blanket of filled earth, usual in similar cases, was prohibited owing to the close proximity of the docks.
The East Boston tunnel, built in 1901, was the first important example of a shield-built monolithic concrete arch, and extends from the Boston subway to East Boston. It is 1.4 m. long, 3,400 ft. being under the harbour. One mile was excavated by tunnel ling with roof shields about 29 ft. wide, through clay containing pockets of sand and gravel. The shields reacted against iron bars set in the concrete and moved forward on the masonry side walls. The engineer was H. A. Carson, and the contractors the Boston Tunnel Construction Company and Patrick McGovern.
A number of tunnels of marked importance, of the subaqueous shield-driven type, operated solely with electric cars (see TRAC TION, ELECTRIC) in addition to the Hudson and Manhattan tun nels already mentioned, have been built under the East and Hud son rivers at New York. They are divided into two groups: those built as parts of the Pennsylvania-Long Island railroad sys tems, and those forming parts of the rapid transit system built by the City of New York.
Of the rapid transit tunnels, the first two tubes, of 15 ft. 6 in. interior diameter and 4,150 ft. long, penetrate gneiss, sand and gravel directly under the East river, between the Battery, in Man hattan, and Joralemon street, Brooklyn. They were begun in 1902, with Wm. Barclay Parsons (and later George S. Rice) as chief engineer, and were finished in Dec. 1907, under the direction of Walton I. Aims and D. L. Hough of the New York Tunnel Com pany, contractors. Two other tubes, also of the same size, built (also through gneiss, sand and gravel) between 1905 and 1907 by the Degnon Contracting Company, with R. A. Shailer as the con tractors' engineer, extend from 42nd street, Manhattan, to Long Island City. These tubes were built as an independent line, but were bought and merged with the rapid transit system, under the operating contracts of 1913. Under these contracts four other tunnels each consisting of two tubes, were also driven beneath the East river : from Whitehall street, Manhattan, to Montague street, Brooklyn; Old Slip, Manhattan, to Clark street, Brooklyn; 14th street, Manhattan, to North 7th street, Brooklyn; and from both street, Manhattan, to Long Island city. They are of larger size. At the 60th and 14th street tunnels the tubes in part are above the original river bed and were built in an artificial but permanent bed of clay protected by rip-rap of stone. On both the Joralemon and Whitehall street tunnels blow-outs of compressed air occurred during construction which carried workmen through to the river surface, and in each case one man survived without injury. (See Plate, fig. 6.) The chief engineer for the city was Alfred Craven, and, later, Daniel L. Turner. The work was done between 1914-2o. Under contracts let by the city for a proposed independent rapid transit system for municipal operation (Robert Ridgway, chief engineer for the board of transportation, City of New York), two other tube tunnels are in process of construc tion (1928) under the East river: Fulton street, Manhattan, to Cranberry street, Brooklyn; and Fifty-third street, Manhattan, to Long Island City. The 53rd street tunnel is also being built in part in an artificial river bottom of clay filling. A tunnel is also being built under the Harlem river, from Manhattan to the Bronx, at 145th street. The greatest shield progress, that on the White hall-Montague street tunnel, was 95 ft. in a week of six working days. A pressure of 48 lb. was used in the 6oth street tunnel.