Page:Encyclopædia Britannica, Ninth Edition, v. 20.djvu/257

Rh RAILWAY 239 ments, to enable the signalmen to communicate with each other, and to have a constant record on the faces of the instruments to show what is being done. METROPOLITAN RAILWAYS. Railways designed for the local service of large cities are neces- sarily either sunk below or raised above the level of the streets. The late Mr Charles Pearson, solicitor to the City of London, was the originator of the system of iutra-inetropolitan railways. He worked at the subject from the year 1837. The Metropolitan and the Metropolitan District Railways in and around London are ex- amples of the underground system. In 1854 the first Act of Parlia- ment was passed ; the works were commenced in 1860 ; the first section of the line Paddington to Farringdon Street was opened in January 3863, Mr John Fowler being the engineer. Several con- secutive extensions into the City and towards Westminster and the Mansion House were made at different times, iintil the "inner circle " was completed in October 1884, thirty years after the passing of the first Act, and twenty-four years after the commencement of the work of construction. The inner circle of railways as con- structed is the direct outcome of the recommendation of the Lords' Committee of 1863, that they should abut upon, if they did not actually join, nearly all the principal railway termini in the metro- polis, completing the circle by a line on the north side of the Thames. The total length of the inner circle is 13 miles and 176 yards. About 2 miles of this length are laid with four lines of rails, and there are twenty- seven stations on the circle at an average distance of half a mile apart. The combined length of the two systems, including the extensions beyond the inner circle, amoiinted in December 1883 to 40 miles. The cost of the Metropolitan Railway system, 22 miles in length, in December 1883 has already been stated as 500,000 per mile, and that of the Metropolitan District Railway system, 18 miles in length, as 374,000 per mile. In 1871, when the works had been completed and opened from Moorgate Street to Mansion House station, the capital expenditure by the District Railway Company for works and equipment of 7J miles of double-line railway was officially stated to be 5,147,000 ; and by the Metropolitan Railway Company 5,856,000 on 10| miles, subject to deduction in respect of surplus lands. The combined cost for 17 miles was at the rate of 630,000 per mile the greater cost per mile being, no doubt, due to the greater proportion of underground work. The cost of the 1^ miles recently opened between Mansion House and Aldgate stations was about 450,000, or about 400,000 per mile. The longer axis of the inner circle is about 5^ miles in length, east and west, and the shorter about 2 miles long at the widest part, north and south. The line runs at very various levels, traversing the sloping ground that stretches from the river Thames towards the heights of Hampstead and Highgate. Several natural sewers, formerly clear brooks or tidal channels, now covered, are traversed by the railway. They occasioned many difficulties and great out- lay, as they required to be conveyed across the line in specially con- structed conduits. The Ranelagh sewer, for instance, is carried under the Metropolitan Railway at Gloucester Terrace" in a brick- built channel 9 feet wide by 8 high ; and over the District Railway at Sloane Square station in a cast-iron tube 9 feet in diameter, supported on wrought-iron girders of 70 feet span. The Fleet Ditch had to be crossed five times. The average level of the rails of the District Railway, which traverses the old bed of the river and the swamps of Pimlico and Bridge Creek, is 13 feet below Thames high- water mark ; whilst that of the northern part, on the Metropolitan Railway, is 60 feet above that datum, making 73 feet of difference of level, and giving rise to heavy works and steep gradients at the west and east ends of the circle. Cuttings 42 feet deep and a tunnel 421 yards in length are found at Campden Hill on the west ; and cuttings 33 feet deep and a tunnel 728 yards in length at Clerken- well on the east, on gradients of 1 in 75 and 1 in 100 respectively. The works of construction consist of covered ways, tunnels, and open cuttings with retaining walls. The cost of property precluded the use of ordinai-y open cuttings with slopes. The covered ways were formed by making open cuttings in the first place and then building "open" or artificial tunnels, and covering them in, so as to restore the surface. The sides of the cuttings were made vertical or nearly vertical, and they were siTpported by timber framing or poling boards till the masonry of the tunnel was completed. The line from Paddington to Moorgate was made in this way with a mixed gauge that is, the 7 feet gauge and the 4 feet 8| inch gauge in combination to take the traffic of the Great Western Railway as well as that of national gauge lines. The covered way was therefore made 28 feet wide and 17 high for the mixed gauge, and the arch is elliptical, built of seven " rings " or courses of brick, with side walls _three bricks or 27 inches thick, on footings 4 feet wide. At the junction of a branch with the main line a "bell- mouth " or expanding arch was constructed in which the span was gradually enlarged to 60 feet. The covered way on the extension, where the national gauge alone was laid, was "25 feet wide. The normal or standard type of arched covered way is 15 feet 9 inches high above the level of the rails. The side walls are three bricks or 27 inches in thickness, and the backs of the walls are earned down vertically to the foundation. The arch was ordinarily built with five rings of bricks, making 22 inches of thickness ; but the number of rings was increased occasionally to eight, nine, or ten rings. The haunches of the arch are backed with concrete. The footings of the walls rest on concrete fcmndations 30 inches in thick- ness. A drain-pipe 18 inches in diameter is laid longitudinally along the middle of the tunnel. The whole of the tunnelling of the District Railway, of which Mr Fowler was the engineer, was put in with open cuttings. Two trenches 6 feet wide were sunk to receive the side walls, which were built up to a level 4 feet above the springing of the arch. As the construction of the walls pro- ceeded the timbering was removed and replaced by concrete backing behind the walls. The earth in the middle, called the " dumpling " or core, was excavated to such a level as to admit of the centering being put into position for the turning of the arch. When the arch was built and the centering removed, the dumpling, which had been utilized for transport, was excavated down to the floor -level from the ends, whence the stuff was conveyed away. By this economical method of procedure the only earth and gravel that required to be lifted was that which was excavated in forming the trenches for the side walls. It was raised by means of steam- cranes travelling on temporary rails laid by the sides of the excavations. Again, the centering for the arch was supported on the core, and was simple and less costly than ordinary centering. The complete arch is shown in section in fig. 23. Inverts, or in- verted arches, were laid in across the bottom, between the footings of the walls, where, from the nature of the soil or from excessive Fig. 23. Fig. 24. FIG. 23. Metropolitan District Railway. Type section of covered way; brick arch. Fia. 24. Metropolitan District Railway. Type section of covered way. lateral pressure, the floor was thought likely to rise. When there was not sufficient depth for a brick arched way the side walls were made, as shown in fig. 24, of brick and concrete, in bays 8 feet wide, of piers and recesses^ spanned by cast-iron girders from 18 to 30 inches in depth, carrying jack-arches between them. The average cost of the arch-covered ways, 25 feet wide, was about 40 per lineal yard, as against 52 per yard for the girder-covered way. On the inner circle there are three tunnels, the Clerkenwell Inner tunnel, 728 yards long, of which the level of the rails was from circle. 29 to 59 feet below the surface of the ground; the "widening" tunnel, 733 yards long, parallel to the Clerkenwell tunnel ; and the tunnel under Campden Hill, 421 yards in length. Even when the utmost precautions are taken, tunnelling through a town is a - risky operation. Settle- ments may occur years after the completion of the works ; water mains may be broken in the streets and in the houses ; stone staircases may fall down ; and other un- pleasant symptoms of instability may show themselves. The cost of the tunnel of 25 feet in width was at the rate of 63 per lineal yard. Open cuttings are 28J feet in clear width on the original line of mixed gauge and 25 feet wide on the extensions. The retaining walls are of FIG. 25. Metropolitan District Railway. Type brick and concrete, in section of open cutting. 11 feet bays, consisting of piers 3 feet wide on the face, and recesses between the piers 8 feet wide. They are inclined backwards with a batter of 1| inches to 1 foot. The foundations are 5 feet below the level of the rails, and the thickness of the walls at the base is 40 per cent., or two-fifths of the height. Occasionally, where the depth is considerable, the thickness is less, and one or two rows of