GREAT TUNNELS OF THE WORLD
Primitive Tunneling—Hoosac Tunnel—Croton Aqueduct—Great Alpine
Tunnels—New York Subway—McAdoo Tunnels—How Tunnels are Built.
The art of tunnel construction ranks among the very oldest in the world, if not the oldest, for almost from the beginning of his advent on the earth man has been tunneling and boring and making holes in the ground. Even in pre-historic time, the ages of which we have neither record nor tradition, primitive man scooped out for himself hollows in the sides of hills, and mountains, as is evidenced by geological formations and by the fossils that have been unearthed. The forming of these hollows and holes was no indication of a superior intelligence but merely manifested the instincts of nature in seeking protection from the fury of the elements and safety from hostile forces such as the onslaughts of the wild and terrible beasts that then existed on the earth.
The Cave Dwellers were real tunnelers, inasmuch as in construction of their rude dwellings they divided them into several compartments and in most cases chose the base of hills for their operations, boring right through from side to side as recent discoveries have verified.
The ancient Egyptians built extensive tunnels for the tombs of their dead as well as for the temples of the living. When a king of Thebes ascended the throne he immediately gave orders for his tomb to be cut out of the solid rock. A separate passage or gallery led to the tomb along which he was to be borne in death to the final resting place. Some of the tunnels leading to the mausoleums of the ancient Egyptian kings were upwards of a thousand feet in length, hewn out of the hard solid rock. A similar custom prevailed in Assyria, Mesopotamia, Persia and India.
The early Assyrians built a tunnel under the Euphrates river which was 12 feet wide by 15 high. The course of the river was diverted until the tunnel was built, then the waters were turned into their former channel, therefore it was not really a subaqueous tunnel.
The sinking of tunnels under water was to be one of the triumphs of modern science.
Unquestionably the Romans were the greatest engineers of ancient times. Much of their masonry work has withstood the disintegrating hand of time and is as solid and strong to-day as when first erected.
The "Fire-setting" method of tunneling was originated by them, and they also developed the familiar principle of prosecuting the work at several points at the same time by means of vertical shafts. They heated the rock to be excavated by great fires built against the face of it. When a very high temperature was reached they turned streams of cold water on the heated stone with the result that great portions were disintegrated and fell off under the action of the water. The Romans being good chemists knew the effect of vinegar on lime, therefore when they encountered calcareous rock instead of water they used vinegar which very readily split up and disintegrated this kind of obstruction. The work of tunneling was very severe on the laborers, but the Romans did not care, for nearly all the workmen were slaves and regarded in no better light than so many cattle. One of the most notable tunnels constructed by the old Romans was that between Naples and Pozzuoli through the Posilipo Hills. It was excavated through volcanic tufa and was 3,000 feet long, 25 feet wide, and of the pointed arch style. The longest of the Roman tunnels, 3-1/2 miles, was built to drain Lake Fucino. It was driven through calcareous rock and is said to have cost the labor of 30,000 men for 11 years.
Only hand labor was employed by the ancient people in their tunnel work. In soft ground the tools used were picks, shovels and scoops, but for rock work they had a greater variety. The ancient Egyptians besides the hammer, chisel and wedges had tube drills and saws provided with cutting edges of corundum or other hard gritty material.