CHAPTER IV
TUNNELS
Their Use in Reducing Grades—The Hoosac Tunnel—The Use Of Shafts—Tunnelling Under Water—The Detroit River Tunnel.
Sometimes the construction engineer of the railroad brings his new line face to face with a mountain too steep to be easily mounted. Then he may prepare to pierce it. Tunnels are not pleasant things through which to ride. They are, moreover, expensive to construct, and when once constructed are an unending care, necessitating expensive and constant inspection. But—and that “but” in this case is a very large one—they reduce grades and distances in a wholesale fashion; and when you reduce grades you are pretty sure to be reducing operating expenses. A railroad man will think twice in his opposition to a smoky bore of a tunnel that will cost some three to five million dollars, when his expert advisers tell him that that same smoky bore will save him a hundred thousand tons of coal in the course of a year.
From almost its very beginnings the American railroad has been dependent upon tunnels, and thus has closely followed European precedent. The Alleghany Portage Railroad, to which reference has already been made, passed through what is said to have been the first railroad tunnel in the United States. It pierced a spur in the Alleghany Mountains, and it was 901 feet in length, 20 feet wide, and 19 feet high within the arch, 150 feet at each end being arched with cut stone. The old tunnel, built in 1832, which has not echoed with the panting of the locomotive for more than half a century, is still to be found not far from Johnstown, Pa. It simply serves the purpose to-day of calling attention to the durable fashion in which the earliest of our railroad-builders worked.
Of the building of the Baltimore & Ohio, tunnel-construction formed an early part, several paths being found across the steep profiles of the Alleghanies. The Kingwood Tunnel, which B. H. Latrobe drove, was nearly a mile long and the chief of these bores. But when the Hoosac Tunnel was first proposed—piercing the rocky heart of one of the greatest of the Berkshires—the country stood aghast. Four miles and a half of tunnel! That seemed ridiculous away back in 1854, when the plan was first broached and folk were not slow to say what they thought of such an absurd plan. For twenty years it looked as though these scoffers were in the right—the work of digging that monumental tunnel was a fearful drain on the treasury of the commonwealth of Massachusetts, which was lending its aid to the project. But the tunnel-diggers finally conquered—they almost always do—and the Hoosac remains to-day the greatest of all mountain tunnels in America. The system of continuous tunnels, by which the Pennsylvania Railroad recently reached its terminal in New York, stretches from Bergen Hill in New Jersey to Sunnyside, Long Island, a distance of some ten miles. In fact the largest feature of recent tunnel-work in this country has been in connection with terminal and rapid-transit development in the larger cities. For a good many years New York and Baltimore, in particular, have been pierced with these sub-surface railroads; it is a construction feature that increases as our great cities themselves increase. No river is to-day too formidable to be conquered by these underground traffic routes. A river such as the Hudson or the Detroit may sometimes halt the bridge-builders; it has but slight terror for the tunnel engineers.
The tunnel-work is apt to be a separate part of the work of building a railroad. It calls for its own talent, and that of an exceedingly expert sort. If the tunnel is more than a half or three-quarters of a mile long it will probably be dug from a shaft or shafts as well as from its portals. In this way the work will not only be greatly hastened but the shafts will continue in use after the work is completed as vents for the discharge of engine smoke and gases from the tube. The work must be under the constant and close supervision of resident engineers. The survey lines must be corrected daily, for the tunnel must not go astray. It must drive a true course from heading to heading. In the shafts plumb lines, with heavy bobs, to lessen vibration, will be hung. Sometimes these bobs are immersed in water or in molasses.
From the portals and from the bottoms of the shafts the headings are driven. If the tunnel is to accommodate no more than a single track it will be built from 15 to 16½ feet wide, and from 21 to 22 feet high, inside of its lining; so the general method is first to drive a top heading of about 10 feet in height up under the roof of the bore. The rest of the material is taken out in its own good season on two following benches or levels.
Piercing a granite mountain is no rapid work. When the Pennsylvania Railroad built its second Gallitzin Tunnel in 1903, 13 men, working 4 drills in the top heading, were able to drill 16 holes, each 10 feet deep, in a single day. The engineers there figured that each blast removed twenty-three cubic yards of the rock. At night, when the “hard-rock men” were sleeping and their drills silent, a gang of fourteen “muckers” removed the loosened material.