NOTABLE TUNNELS. The number of tunnels notable because of their length, the difficulties encountered in their construction or for other reasons, has become so great that mention can be made here of only a few of those which are most celebrated. The Mont Cenis Tunnel through the Alps places France in direct communication with Italy. It passes from a point near Alodane, in France. under the Col he Fr('jns, about 18 miles west of the actual Mont Cenis, into Italian territory, at a point near Bardo necchia. about 24 miles from Susa. The length of the tunnel between extremities is 7.6016 miles. It is formed with a gradient from each end, at the rate of about 1 in from Modane and I in 2000 from Bardoneechia. the summit or meeting of the gradients being half way through the tunnel. The railway does not enter at the ex tremities of the tunnel, but joins it by means of special curved sections of tunnel at each end. The total length of tunnel traversed by trains is 7.9506 miles. The following is the for mation of the rode traversed by the direct tunnel advancing from the north end: Carbonaceous schist, 1.3027 miles; quartz. 0.2414 mile; lime stone, 0.2210 mile; calcareous schist, 5.8365 miles. The tunnel on leaving Modane is of the following dimensions: 25 feet inches wide at the bottom, 26 feet inches wide in the broad est point, and 24 feet inches high, the arch being semicircular. At Bardoneechia the height is greater by 11'4 inches and the arch is made elliptical to enable it to resist the greater strain caused by a different inclination of the strata. The tunnel is lined with the exception of about 300 yards on the north side. The side walls are S feet 6 inches thick throughout. The arch to the south side is constructed principally of brick, and to the north side of stone, a brick key being applied throughout. There are side paths of flagstones 20 inches wide.
Work was begun in 1837. and for three years hand labor was used entirely, but it was planned from the beginning by the engineers, Sommeiler, Grandis, and Grattoni, to introduce machinery ultimately. In 1861 power drills were put at work at the south end, and in 1S62 the north end was similarly equipped. The drills used were operated by compressed air and they and also the compressors used were invented by Sommelier. The tunnel was completed and opened for traffic in 1872. In 1872, however, work was begun on the Saint Gotthard rail way tunnel through the Alps between Italy and France, which far exceeded the Mont Cenis in magnitude. This tunnel crosses the moun tains between Goescheuen and Airolo, and is 9.25 miles long. The excavation was through rock consisting chiefly of gneiss, mica schist, serpen tine, and hornblende, the strata having an incli nation of from 45° to 90°. At many points the
rock was fissured and disintegrated easily, and water was encountered in large quantities. caus ing much trouble. In this work, as at Mont Cenis, power drills and compressed air were used, but in a much improved form as a result of the pre vious experience and years of study. The exca vation was lined throughout with masonry, the side walls being of rubble stone and the roof arch of brick. Along the bottom there was a cul vert of brickwork. The Mont Cenis Tunnel had been excavated by means of a drift as an ad vance gallery, but at Saint Gotthard the advance gallery was a top centre heading. Water power, secured by draining near-by mountain torrents, was used to compress the air used in operating the drills and for driving the compressed-air locomotives used in hauling the debris from the excavation. The tunnel was opened for traffic in 1882.
The third great Alpine tunnel is the Simplon Tunnel, nearing completion in 1904. Many schemes for the connection of Italy and Switzer land by a railway near the Simplon Road Pass have been devised. The scheme which was put forward in 1881 by the Jura-Simplon Railway consisted broadly of piercing the Alps between Brigue, in the Rhone Valley, and Iselle. on the Italian side, from which village the railway de scends to the southern terminus at Domo d'Os sola, a distance of about 11 miles. Starting from Brigue. the new line, running gently up the val ley for miles, on account of the proximity of the Rhone. enters the tunnel on a curve to the right of 1050 feet radius. At a distance of 153 yards from the entrance the straight por tion of the tunnel commences, and extends 12 miles. The line then curves to the left with a radius of 1311 feet before emerging. Commenc ing at the northern entrance, a gradient of 1 in 300 miles for a length of miles to a level length of 550 yards in the centre, and then a gradient 1 in 143 descends to the Italian side. The tunnel will be a double tunnel. That is, there will eventually be two parallel tunnels, having their centres 50 feet apart, each carrying one line of railway ; but at the present time only one tunnel. that known as No. 1, has been excavated to full size. No. 2 being left, masonry lined where necessary. for future developments. By means of cross-headings every 220 yards, the problems of transport and ventilation are greatly facilitated. in cross-section tunnel No. 1 is 13 feet 7 inches wide at the bottom, and 16 feet 5 inches wide at the widest part, with a total height of IS feet above rail-level. The material penetrated is rock. Rotary drills operated by hydraulic pressure were used, there being an elaborate water-power plant at each end of the tunnel.