RAILROAD TUNNELS.
The establishment of railroad communication has given rise, both in this country and Europe, to some stupendous undertakings in the way of tunneling; one or two of which are worthy of notice as illustrating the nature and extent of this kind of work. And the first of these which we shall mention, and one of the most remarkable, is the Box tunnel on the Great Western railway in England. This tunnel pierces what is called Box hill, between Chippenham and Bath, part of which is four hundred feet above the level of the track. It is ninety-six hundred and eighty feet long, thirty-nine feet high, and thirty-five wide to the outside of the brick-work. The shafts for making and ventilating it, are thirteen in number, and vary in depth from eighty to three hundred and six feet. The excavation amounted to four hundred and fourteen thousand cubic yards; and the brick-work and masonry, to more than fifty-four thousand cubic yards. The number of bricks used, was thirty million. A tun of gunpowder and a tun of candles were consumed every week for two years and a half; and eleven hundred men and two hundred and fifty horses were kept constantly employed for all that time. For a considerable distance the tunnel passes through freestone rock, from the fissures of which there was, at times, an immense influx of water, by which on one occasion the works were interrupted for a period of nine months. On another occasion after an irruption, water was for some time discharged by the engine at the rate of thirty-two thousand hogsheads a day. This tunnel is on an inclined plane of one in a hundred. There are several other tunnels of great extent in England, such as the Kilsby tunnel, on the London and Birmingham road, which is over seven thousand feet long; and the tunnel from Wapping to Edge hill, on the Liverpool and Manchester road, which is over six thousand feet long, and quite a number of others of five thousand, four thousand, three thousand feet long, &c. One of these remarkable tunnels, is that on the South-eastern or Dover railway, a view of which is given in the cut on the following page, which passes through what is called Shakspeare’s cliff, at Dover, (though the cliff to which the poet alluded has been undermined and thrown down, and the name is now given to another part of the same range,) on the north side of the British channel. This cliff is a high bluff of chalk, on the west of the town, the white appearance of which gave the name of Albion (white) to England. There are two openings in the tunnel; and through these the whizzing locomotives fly along the dizzy precipice, as if it were an ordinary highway. There is, also, a second tunnel in the same cliff. This last is called the Abbot’s-cliff tunnel, and is about a mile in length, coming out on the face of the rock about sixty feet above the sea. The track passes along the front of the rampart for about a mile, and then enters the Shakspeare tunnel, which is also about a mile in length. Thence, again, it issues on the face of the cliff, and proceeds to the station at Dover.
TUNNEL IN SHAKSPEARE’S CLIFF.
In the United States there are quite a number of railroad tunnels of great extent. One of these is the Blue Ridge tunnel, in Virginia, the length of which, when completed, will be forty-two hundred and sixty feet, of which more than half is already (1855) finished. The work has been commenced on each side of the mountain, and is progressing at the rate of about fifty feet a month, at which rate of progress it would take about three years to complete it.
But probably the most gigantic work ever proposed in the way of tunneling, is the Hoosic tunnel, on the line of the Troy and Greenfield railroad, by which it is designed to shorten the passage from the former place to Boston. This immense tunnel it is proposed to carry through the solid rock of the mountain for a distance of some four miles, and to make it wide enough for a double track for the railroad; the expense of doing which is variously estimated, at from four million to six million dollars. By the ordinary method of drilling and blasting, it would take so long a time, and require so large an expenditure, that all idea of thus accomplishing the work has long since been given up, if, indeed, it was ever entertained. And the plan is, by immense boring machines, constructed for the purpose, to make grooves round large masses of the rock, and when these latter are broken up by blasting, to remove them piece by piece. Several such machines have been invented and constructed with reference to this very work, and one or two of these have been found successful in practice, though the immense strain caused by the boring is such as to require corresponding strength in the borer. To give the necessary ventilation, and now and then light to the tunnel, both when in the course of construction, and especially when finished and in use, it is proposed at proper intervals to sink dry wells, or openings from the top of the mountain, down to the tunnel itself; so that the constant stream of air entering the mouth of the latter, at either end, may be always and steadily passing up through these chimneys or ventilators, thus carrying off the smoke of the engines, or any impurities of the otherwise stagnant air. The work, when completed, if it ever is, will be a monument of enterprise and perseverance, unrivaled in the history of tunneling in this or any other country of the world.