Tunnel

an underground passage. The oldest tunnels known are those of Egypt and India. They were used for tombs and temples. The Romans tunneled to drain lakes, to straighten their highways, and to construct sewers. The French built a number of tunnels through which to lead canals. The aqueducts of the ancients were led, not infrequently, through tunnels constructed in the solid rock.

Wherever tunnels pass through loose earth or crumbling rock it is necessary to prevent caving by walls of timbers or of masonry. The first tunnel in the United States was built at Auburn, Pennsylvania, in 1821, to permit the passage of coal barges. Well known American tunnels may be mentioned: That under the St. Clair River at Detroit, for the Grand Trunk Railway; the Croton Aqueduct tunnel, thirty-one miles long, at New York City; the Hoosac Tunnel of western Massachusetts; the tunnels of the Northern Pacific Railway and of the Great Northern Railway in the Cascade Mountains; the Sutro Tunnel, leading into the mines of the Comstock Lode of Nevada; the tunnels of the New York underground tramways; the East Boston tunnel for street railways, etc. Submarine trolley and railway tunnels are now in process of construction from Staten Island to Long Island and to the New Jersey shore. The double tunnel of the Pennsylvania Railway, through the mud of the Hudson River, consists of two huge parallel tubes of boiler iron lined with concrete. The construction of such a tunnel presents great difficulty and danger. A huge nozzle or shield is advanced slowly, while workmen remove the earth and mud inside of it and build the tunnel behind it. The shield in which the men work is filled with compressed air, which prevents the inflow of water or mud that otherwise would fill the shield. Workmen suffer terribly from the effects of the air pressure and many lose their lives.

See Hoosac; Cenis; Simplon; St. Gotthard; Cloaca Maxima; Aqueducts; Subway; Niagara Falls

In boring tunnels, the Roman engineers worked simultaneously from both sides of the mountain, in the same way that modern engineers do. In 1860 an inscription was discovered which contains a curious report of an engineer who had in charge the construction of an aqueduct tunnel for the town of Saldae, in Algeria. During his absence the boring went awry, and the ends of the sections could not be brought together. The engineer was sent for. His report says: "I found everybody sad and despondent; they had given up all hopes that the two opposite sections of the tunnel would meet, because each section had already been excavated beyond the middle of the mountain, and the junction had not yet been effected. As always happens in these cases, the fault was attributed to the engineer, as though he had not taken all precautions to insure the success of the work. What could I have done better? I began by surveying and taking the levels of the mountains; I marked most carefully the axis of the tunnel across the ridge; I drew plans and sections of the whole work, which plans I handed over to Petronius Celer, then governor of Mauritania; and to take extra precaution, I summoned the contractor and his workmen, and began the excavation in their presence. . . . Well, during the four years I was absent, expecting every day to hear the good tidings of the arrival of the waters at Saldae, the contractor and the assistant had committed blunder upon blunder; in each section of the tunnel they had diverged from the straight line, each towards his right, and, had I waited a little longer before coming, Saldae would have possessed two tunnels instead of one."--Lanciani's Ancient Rome in the Light of Recent Discoveries.