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.
[Illustration: 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.