TUNNEL. 546 TUNNEL. 1897. A single electric railway track in each tunnel forms a double-track railway between the termini named. The Central London Railioay runs from Shepherds Bush to the Bank, a dis- tance of 5 1 miles, the whole distance being in deep tunnel at depths varying from 00 to 90 feet. It consists, like the two roads previously mentioned, of two parallel circular tunnels. Each tunnel is 11% feet in diameter and has a cast- iron lining. The shield system of construction was employed. To be added to these tunnels are the Metropolitan District railways, parts of which are underground, begun in 1853, the Waterloo and Baker Street Railway, and the projected Euston and Hempstead Railway. The longest of the London tunnels is the Blackwall Tunnel for street traffic under the River Thames. The total length of this work is 6200 feet, of which 3088 feet are tunnel proper, 1370 feet are open cut roofed over, and 174i2 feet are open cut without covering. The exterior di- ameter of the tunnel is 27 feet. It was driven by means of a shield 27 feet 9 inches in diameter and IS<2 feet long, with two diaphragms, from horizontal partitions or stages and four vertical partitions. The lining is of cast-iron rings. Work was begun in 1892 and completed in 1897. The tunnel provides a roadway 16 feet wide and two sidewalks each 3 feet IVa inches wide. In Glasgow, Scotland, the Glasgow Citij and District Railu-ay has a length of 3.123 miles. Of this dis- tance one Uiile is deep tunnel, and 3483 feet are tunnel built by the open-cut method. Work was begiui in lS83"and complelcd in 1886. The Glas- gow Central I'ailuay has 0.84 of a mile of deep tunnel and 3.13 miles of open-cut tunnel. The Glasgow District >Siihway, HVa miles long, con- sists of two parallel circular cast-iron lined tun- nels 11 feet in interior diameter. The tunnels were driven by the sliield method. Construction was begun in 1891 and completed in 1894. The Metropolitan Railway of Paris, comprising alto- gether some 40 miles of projected railway, com- pleted in 1900 the main line from the Porte de Vincennes to the Porte JIaillot and the Porte Dauphine, 8.7 miles. This is entirely underground. In the tunnel excavation the Berlier type of shields ordinarily were used ; but progress by this means was found too slow', and open, timbered excavation of the ordinary type was employed. The so-called Belgian method of tunneling was used; the arch was first built and then the side walls were erected by underpinning the arch. After the earthen core was removed the bottom arch, or invert, was set in place. At the stations, however, the side walls were first con- structed and upon them the arch, or metallic roof, was built. The removal of the earth from the core then took place, as in a tunnel, and the last stage was the construction of the invert. The line is double-track electric railway throughout. The Boston Subway, begun in 1894, is prac- tically the underground tunnel of the surface electric lines entering the business district of the city of Boston. The portion of the line completed in 1898 was 10.810 feet long, divided between double-track and four-track tunnel. The bulk of the tunnel was built by open-cut methods, but on certain portions the shield system was employed. In 1900 work was begun on a IVi- mile extension of the original line under Boston Harbor to East Boston. The East Boston tunnel has a polycentric cross-section 2314 feet wide and 20Vi feet high and is lined with concrete masonry. The double-track subway section is appro.ximately rectangular and 24 feet wide by 14 feet high, while the four-track section is a similar form, but twice as wide. The lining con- sists of concrete side walls and brick roof arches supported by colunms and I-beams of steel. The Sew York Subway, as contracted for in 1899, comprises some 20)^ miles of line, three- fourths of which is in tunnel. A four-track line runs from the City Hall to 103d Street, and there divides into two double-track lines running to Bronx Park and to Kingsbridge, resiiectively. The cross-section of the underground line is of did'erent types, as indicated on the plate. In the rectangular section used for more than half of the line, the dimensions adopted for two tracks are 25 X 13 feet, and for four tracks, 50 X 13 feet. The barrel-vault section, composed of a polycentric arch, is usually 24 feet wide and 10 feet higli. The circular sections are 15 feet in diameter, two tunnels being built side by side for double-track line. The work was done partly bj- open-cut methods and partly underground, ac- cording to the depth of the line below the surface. Among other notable tunnels the following may be briefly mentioned: Arlbcrg Tunnel, in Austria, begun in 1880 and completed in 1884 for a double-track railway, 6.38 miles long. Tctjuix- quiac Tunnel, begun in 1888 to drain the valley of Mexico, 6 miles long and about 14 feet wide and 14 feet high, completed in 1898. Trans- Andean Railway Tttnncl, through the summit of the Andes on the railway line between Buenos Ayres and Santiago, three miles long, at an elevation of 10,460 feet above the sea. First Thames Tunnel at London, England, begun in 1825 and completed in 1843, 1200 feet long with two parallel ways of horseshoe section, each 13% feet wide and 16^; feet high. East River Gas Tunnel, between New York and Brooklyn, 2516 feet long and 10 feet 2 inches in diameter, be- gun in 1892 and completed in 1894. Khojak Tunnel, on the Northwestern State Railway in India, 12,870 feet long, begun in 1889 and com- pleted in 1891. Strickler Tunnel, for the water supply of Colorado Springs. Colo., 6441 feet long, "with a section 4X7 feet through the rock. Oraveh(il~ Tunnel, on the Bergen Railway, in Nor- way, single track, 17,400 feet long. Busk Tunnel, on the Colorado Midland Railway, in Colorado, 9094 feet long, with a section 15 feet wide and 21 feet high through rock. Bibliography. The literature on tunneling which is readily available is exceedingly limited. The most comprehensive book on the subject is Drinker, Tunneling (New York. 1874), which is now out of print. The book which ranks next in importance is Simms, Practical Tunneling (ib., 1896). The most recent book on the subject is Prelini, Tunneling (ib., 1901), which is a thor- oughly up to date text-book of some 300 pages. Legouez, De I'emploi du boudier dans la con- struction des souterraines (Paris, 1897), is a comprehensive treatise on the shield system of tunneling. Among the works describing individual tunnels are: Von Rosenber?. The Vorburg Tunnel (New Y'ork, 1887) : Walker, The Severn Tunnel (London, 1888) ; Burr, Tun- neling Under the Hudson River (New York, 1885); Sutro, The Sutro Tunnel (ib., 1887).
