The Liberty vehicular tunnels penetrate the south hills at Pitts burgh, Pa., and connect with the Liberty bridge, over the Monon gahela river. They consist of two parallel tunnels, 59 ft. between centres, each 26 ft. 7 in. wide, and Di m. long. Each tunnel pro vides a single line of street railway track not installed and two lines of vehicular traffic on a roadway 21 ft. wide. There is also a foot-walk, 4 ft. wide, in each tunnel. The tunnels are lined with concrete 24 in. thick. The alignment is straight and the grade continuous at the rate of 0.392%. The work was begun in 1919 and completed about three years later. The total cost was about $6,000,000. For tunnels of their size, unusually rapid progress was made in excavating which was due largely to a bonus system of paying the workmen. Eleven hours' pay was allowed for 9 ft. advance of excavation and 12 hours' for io ft., whether consumed or not. There was also sharp rivalry between the forces in the two tunnels, and the men completing their shift first were allowed to display an American flag at the entrance, the following day, while their competitors were compelled to display a black flag. The average rate of advance per day in the tunnels was over io ft. for a period of several months.
The Moffat tunnel, on the Denver and Salt Lake railroad, re places a surface line with 4% grades, crossing the Continental Divide, about so m. west of Denver, Colo. At the time of con struction it was the longest railroad tunnel in America. It lies at an elevation of 9,200 ft. above sea-level, as compared with 11,660 on the surface line at the summit of the Divide. The work was begun in 1923 and the first train was run through in Feb. 1928. The work consists of two parallel tunnels, 75 ft. apart, one for a single track railroad, 16 ft. by 24 ft. and one for a water tunnel, 8 ft. by 8 ft., which may be used for the future water-supply of the City of Denver. The work was done by the Moffat Tunnel Commission, and paid for by a bond issue by a district of the State in the vicinity and the City of Denver. The railroad tunnel is leased to the Denver and Salt Lake railroad. The length of the tunnel is 6.1 m. and the cost including the water tunnel was about $15,470,000. The grades of the railroad tunnel rise from the ends toward the centre, on rates of 0.3% from the east and 0.9% from the west. The construction of both tunnels at one time was taken advantage of to use the water tunnel as a pioneer heading, with cross connections to the main railroad tunnel at intervals of about 1,500 ft., as was done in the Simplon tunnel and the Connaught tunnel at Rogers pass, which offered 'd vantages in speed and ventilation. Chloride of lime dumped in one of the lakes, 1,400 ft. above, was found in the tunnel water two hours later.
The new Cascade tunnel of the Great Northern railway, be tween Berne and Scenic, in the State of Washington, is 7.79 m. long. (See fig. 7.) It is the fifth longest railway tunnel in the world and the longest railway tunnel in America. The alignment is straight and the grade 1.565% downward to the west from Berne. Work was started in Dec. 1925. The tunnel was driven from the two portals and a shaft, 622 ft. deep, 2.41 m. from the east end, by the centre heading method, to allow radial drilling. A pioneer tunnel, 66 ft. to one side and parallel with the main tunnel, was also driven, from which cross-drifts were driven at 1,500 ft. intervals. This provided a number of points of attack and insured proper ventilation and drainage. The pioneer heading has a width and height of io ft. and was advanced 984 ft. in one month. The pioneer heading was holed through in May 1928, and the main tunnel was completed during the same year and put in operation Jan. 12, 1929. The power used in construction was
2,300 volts, 6o-cycle, 3-phase current. The total compressor capacity was 10,450 cu.ft. of free air per minute. Haulage in the headings was by 6-ton, 250-volt trolley locomotives, and for the full section 2o-ton trolley locomotives. The locomotives were equipped with gathering reels, which allowed their working 500 ft. beyond the suspended trolley. The line speed of the skip hoists at the shaft was 90o ft. per minute. A total force was employed of about 1,800 men and, because far distant from any settlement, complete camps with cottages, schools, recreation halls, stores and shops were provided, equipped with water-supply, electric lights, sewers and modern plumbing. J. R. W. Davis is chief engineer for the Great Northern railway, and the contractor was A. Guthrie and Co. The line through the tunnel is to be operated electrically. The estimated cost is $16,000,000. (See TRACTION, ELECTRIC. ) The electric railway from Eiger glacier to near the summit of the Jungfrau includes a tunnel 1.5 m. long, ir ft. io in. wide and 12 ft. 6 in. high, with a midway station having arches through the side 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, may be reached by an elevator.
Among other important rock tunnels may be mentioned the Albula, through a granite ridge of the Rhaetian Alps, for a single track narrow-gauge railroad, 3.6 m. long; the Giovi, 6 m. long, north of Genoa, Italy; 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 Arthur Pass tunnel in New Zealand, begun in 1908, 5.3 m. long, for a single track, narrow gauge railway; the Suram, on the Trans-Caucasus railway, for double track, 2.47 m. long, through soft rock; the Graveholz tunnel, on the Bergen railway, in Norway, 3.3 m. long (the longest in northern Europe) ; the tail-race tunnel for the Niagara Falls Power Company, being 1.3 m. long, 19 ft. wide and 21 ft. high, through argillaceous shale and limestone, costing about $r,250,000; the Tequixquiac outlet to the drainage system for the City of Mexico, 6.2 m. long, costing $6,760,000; the first Cascade tunnel, Washington, part of the Great Northern railway system, 2.63 m. long and saving 9 m. in distance (now replaced by a still longer tunnel, 7.79 m.) ; the Gunnison, 5.8 m. long, irrigating 147, 00o ac. in Colorado ; the double track railway tunnel of the Cana dian Northern railway, under Mount Royal in Montreal, Canada, 3.5 m. long; and the double track Musconetcong tunnel of the Lehigh Valley railroad, a little less than i m. long and costing $5, 000,000, holed through in 21 months (June 1928). An example of a small tunnel of considerable length is the Strickler tunnel. It sup plies water to Colorado Springs, from Pike's peak of the Rocky Mountains, in Colorado. It is 1.22 m. long and the cross-section is only 4 by 7 feet.
For many reasons, including both safety of the work and interest charges on the capital investment, speed in tunnel con struction is desirable, and such work is always pushed as fast as possible. During the World War, the Northern railway of France built the Marseille-en-Beauvaisis tunnel, a single track railway tunnel, paralleling a similar one in operation and 6o ft. from it, at the rate of 16 ft. per day. It is 1,200 ft. long, in badly fissured chalk formation and is lined with concrete. It was begun May 21, 1918, the headings met June i8 and it was in operation Aug. 4, a period of 75 days.