A three-per-cent grade is almost the extreme limit for anything like a profitable operation; even a two-per-cent grade is one in which the operating people look forward to reconstruction and elimination. Yet there are short lengths of line up in the mining camps of Colorado, where grades of more than four per cent are operated; and it is a matter of railroad history that away back in 1852, when the Baltimore & Ohio Railroad was being pushed through toward Parkersburg, and the great Kingwood tunnel was being dug, B. H. Latrobe, the chief engineer of the company, built and successfully operated a temporary line over the divide at a grade of ten per cent—528 feet to the mile. A locomotive which weighed 28 tons on its driving-wheels carried a single passenger car, weighing 15 tons, in safety and in regular operation over this stupendous grade for more than six months. The ascent was made by means of zigzag tracks on the so-called switchback principle. That scheme succeeded earlier planes operated by endless chains; an instance of which is the quite famous road of Mauch Chunk, originally operated for coal, and now a side scenic trip for passengers. Other planes of this sort, you will remember, were in operation at Albany and Schenectady on the old Mohawk & Hudson route, now a part of the New York Central lines; but all of them involved a change of passengers and freight to and from their cars, and the zigzag switchback was considered quite an advance in its day. Two of these ancient switchbacks are still in regular use for passengers and freight—one at Honesdale, Pa., and the other at Ithaca, N. Y.
The matter of grades being settled, and with it as a corrollary the question of minor curves, minor details next claim attention. Perhaps the water supply along the new line is defective. Then arrangements must be made for impounding, and perhaps suitable dams and waterworks will be built for this purpose. The water must be soft, to protect the locomotive boilers; if hard, an apparatus is erected for the softening process. Grade crossings are to be avoided, highway crossings being built, wherever possible, over or under the railroad.
A railroad crossing another railroad at grade is an abomination not to be permitted nowadays. The universal use of the air-brake has permitted a reduction of the “head-room,”—the necessary clearance between the rail and overhead obstruction—from 20 feet to 14 feet. The old “head-room” was necessary to protect the brakeman who worked atop of the box-cars. This reduction of six feet in clearance was a matter of infinite relief to engineers, particularly in the bridging of one railroad over another.
The entire problem of bridges is so intricate a phase of American railroad construction as to demand attention in a subsequent chapter. In actual railroad practice it is apt to demand a separate branch of engineering skill, both in construction and in maintenance. We turn our attention back to the main problem of the building of our railroad.
When all plans are finished, contracts remain to be divided and sub-divided; for it would be a brave contractor, indeed, who in these days would consent to essay himself, any considerable length of railroad line. In fact, in recent work of heavy nature, the price is almost invariably placed at an indefinite figure, a certain definite percentage of profit being allowed the contractor on each cubic yard of rock or soil. In such a case the contractor’s business becomes far less a game of chance; he is, in effect, the railroad’s agent supervising its construction at a certain set stipend.
Let us say that the construction on our railroad begins in the early spring. As a matter of real fact it would not be halted long because of adverse weather conditions. Even up in the frozen and uninhabitable wilds of the Canadian Northwest, work has been prosecuted on the new Grand Trunk Pacific throughout the entire twelve months. But in summer the construction gangs rejoice. The great proposition of bringing mile after mile of future railroad to sub-grade—the level upon which the cross-ties are to be set—fairly sweeps forward under the genial warmth of the sun. The construction is under the supervision of competent engineers, who are, of course, under the direct supervision of the railroad’s own organization. Every six to twelve or fifteen miles of new line is divided into sections, better known as residencies, for each is under the eye of its own resident engineer. He reports to the construction engineer, who in turn reports to the chief engineer of the railroad, an officer who reports to no less person than the president of the company.
This great force—for each engineer has gathered about him a competent staff of young men as expert with compass, with level, and with transit as were the men who first projected the line—is in the field as quickly as the contractor. They are to see him bring the line to sub-grade; to see him place bridges and culverts, bisect high hills with cuttings, bore tunnels through even higher hills and mountains, span deep valleys with great embankments. To facilitate quick construction the residencies are made numerous; work begins at as many initial points as possible. These points, of course, are situated, where possible, close to water communication or existing railroad lines, in order that material may be brought with the least possible delay and expense.
Of course, if the country has a sharp contour, the ordinary difficulties of line-construction multiply very rapidly. The great cuttings through the hills may have to be carved out of resisting rock, a work that is carried on through many levels, known to the engineers as ledges or as benches. If there are high hills to be notched there will probably be great hollows where the circumstances do not justify carrying the line on bridge or trestle. In these cases come the fills, or embankments. We have already shown how the locating engineer in the first instance has tried to plan his line so that the earth or rock from his cutting will be as nearly as possible sufficient to form the near-by embankments. Sometimes it is not, and then the resident engineers must locate borrow-pits, where the hungry demand of the railroad for dirt will cause a great hollow to show itself on the face of the earth. The borrow-pit must be carefully located—convenient of access, far enough from the track not to be a danger spot to it. This is one of the infinity of problems that come to the construction engineer.