Page:EB1911 - Volume 27.djvu/422

Rh tunnel and shafts were opened up 25 to 70 yds. apart, from which smaller headings were driven right and left. The tunnel was enlarged to its full section at different points simultaneously in lengths of 8 yds., the excavation cf each occupying about twenty days, and the masonry fourteen days. Ferroux percussion air-d rills and Brandt rotary hydraulic drills were used, the performance of the latter being especially satisfactory. After each blast a fine spray of water was injected, which assisted the ventilation

FIGS. 7 and 8.-Method of excavation in St Gotthard Tunnel. materially. In the St Gotthard tunnel the discharge of the air-drills was relied on for ventilation. In the Arlberg tunnel over 8000 cub. ft. of air per minute were thrown in by ventilators. To keep pace with the miners, 900 tons of excavated material had to be removed, and 350 tons of masonry introduced, daily at each end of the tunnel, which necessitated the transit of 450 wagons. The cost per lineal yard varied according to the thickness of masonry lining and the distance from the mouth of the tunnel. For the first thousand yards from the entrance the prices per lineal yard were £11 Ss. for the lower heading; £7 12s. for the upper one; £30 IOS. for the unlined tunnel; £45 for the tunnel with a thin lining of masonry; and £124 5s. with a lining 3 ft. thick at the arch, 4 ft. at the sides, and 2 ft. 8 in. at the invert. The Simplon tunnel was begun in 1898 and completed in 1905. It is over 30 % longer than the St Gotthard, and the greatest depth below the surface is 7005 ft. A novel method was introduced in the shape of two parallel bores (56 ft. apart, connected at intervals of 660 ft. by oblique galleries), which greatly facilitated ventilation, and resulted in increased economy and rapidity of construction, while ensuring the health of the men. One of these galleries was made large enough for a single track railroad, and the second is to be enlarged and similarly used. The death-rate in the Simplon tunnel was decreased as compared with the St Gotthard from 800 in eight years to 60 in seven years. Had one wide tunnel been made instead of two narrow ones, it would have been difficult to maintain its integrity; even with the narrow cross-section employed the floor was forced up at points in the solid rock from the great weight above, and had to be secured by building heavy inverts of masonry. Temperatures were reduced to 89° F. by spraying devices, although the rock temperatures ranged from 129° to 130° F. At one point 4374 yds. from the portal of Iselle the “Great Spring” of cold water was struck; it yielded 10,564 gallons per minute at 600 lb pressure per sq. in., and reduced the temperature to 55-4° F., the lowest point recorded. A spring of hot water was met on the Italian side which discharged into the tunnel 1600 gallons per minute with a temperature of 113° F. The maximum flow of cold water was 17,081 gallons per minute, and of hot water 4330 gallons per minute. These springs often necessitated a temporary abandonment of the work. Water power from the Rhone at the Swiss and from the Diveria at the Italian end provided the power for operating all plant during the construction of most of the work. Among the able engineers connected with this work must be mentioned Alfred Brandt, a man of remarkable energy and ability, whose drills were used with much success. He died early in the work, of injuries received from falling rock. A group of tunnels-the Tauern, Barengraben, Wocheiner and Bosrtick-was undertaken by the Austrian government in connexion with new Alpine railroads to increase the commercial territory tributary to the seaport of Trieste, which at onetime was' greater than Hamburg. The principal tunnel of this group is under the main body of the Tauern mountain. The bottom drifts met on the 21st of July 1907. The difficulties resulted mostly from mountain débris and springs. There are four minor tunnels between Schwarzach, St Veit, and the north portal of the Tauern, and nineteen between the south portal and the south slope at Mollbriicken. The electric railway from the Eiger glacier to near the summit of the Jungfrau includes a tunnel 1% m. long, 3-6 metres wide and 3-8 metres high, with a midway station, from which a large part of northern Switzerland can be seen. From the Jungfrau terminus, at an elevation of 13,428 ft., the summit, 242 ft. higher, will be reached by an elevator. The Hoosac tunnel was the first prominent tunnel in America. It was begun in 1855 and iinished in 1876, after many interruptions. It was memorable for the original use in America of air-drills and nitroglycerin. The Pennsylvania railroad tunnels crossing New York City under 32nd and 3 3rd Streets are of unusual size. 0wing»to the close proximity of large buildings and other structures special methods were adopted for mining the rock to lessen the vibrations by explosions. At 33rd Street and 4th Avenue the tunnels pass directly under two of the Rapid Transit system, above which there is another belonging to the Metropolitan Traction Company, so that there are three tunnels at different levels under the street. Among other rock tunnels may be mentioned the Albula, through a granite ridge of the Rhaetian Alps, for arsingle-track narrow-gauge railroad, 3-6 m. long; tunnels on the Midland railway, near Totley in Derbyshire, »over 3-5 m. long, largely in shale, and at Cowburn, over 2 m. long, in shale and harder rock, each 27 ft. wide and 20-5 ft. high inside; the Suram, on the Trans-Caucasus railway, for double track, 2-47 m. long, through soft rock; the tail-race tunnel for the Niagara Falls Water Power Company, 1~3 m. long, IQ ft. wide and 2I ft. high, through argillaceous shale' and limestone, costing about $1,250,000; the Tequixquiac outlet to the drainage system for the city of Mexico, costing $6,760,000; the Cascade, Washington, part of the Great Northern railroad system, saving 9 m. in distance; and the Gunnison, irrigating 147,000 acres in Colorado.

Tunnelling in Towns.-Where tunnels have to be carried through soft soil in proximity to valuable buildings special precautions have to be taken to avoid settlement. A successful example of such work is the tunnel driven in 1886 for the Great Northern Railway Company under the Metropolitan Cattle >|— "" °'°" 7  ""*' °" ';'-1

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