TUNNEL, a subterranean or subaqueous way, constructed for purposes of passage. In mining, the term is often applied to horizontal excavations, especially to such as are known by the designations gangway, heading, drift, and adit, used as underground roads or for the passage of water. (See Adit.) Herodotus mentions a tunnel in the island of Samos, cut through a mountain 150 orygia (900 ft.) high. Its length was seven stadia (4,247 ft.), and its cross section 8 ft. high by 8 ft. wide. In Bœotia a tunnel was constructed for the drainage of Lake Copais. When Cæsar arrived at Alexandria, he found the city almost hollow underneath from the numerous aqueducts; every private dwelling had its reservoir, supplied by subterranean conduits from the Nile. The aqueducts of the ancient Romans, and of the Peruvians and Mexicans, included remarkable tunnels. (See Aqueduct.) Among the many Roman aqueducts on which tunnels were built were the Aqua Claudia, of which 36½ m. passed underground; the Aqua Appia, built in 312 B. C., 11,190 Roman paces in length, 11,130 being underground and arched; and the Aqua Virgo, 14,105 paces long, 12,865 underground. A tunnel was begun in 398 B. C. to tap Lake Albanus, at the instance, Livy tells us, of the oracle of Delphi. It was 6,000 ft. long, 6 ft. high, and 3½ ft. wide. Fifty shafts were sunk on its line, and the work was finished within one year, though it was driven through the hardest lava. A similar work of greater magnitude was undertaken to connect Lake Fucinus (now Celano) with the river Liris (now Garigliano); 30,000 men were employed on it for ten years, and it was finished at a vast expense A. D. 52. A minute account of the modern clearing out of this work by the Neapolitan government may be found in “Blackwood's Edinburgh Magazine,” vol. xxxviii., p. 657. The accuracy of the surveying in these works is astonishing when we consider the rudeness of the instruments. Among those used in levelling by the Romans were the libra aquaria and dioptra, of which we have no clear description. The chorobates seems to have been preferred. It consisted simply of a rod or plank about 20 ft. long, mounted on two legs, at its extremities, of equal length. The rods or legs were secured by diagonal braces, on which were marked correctly vertical lines. A plumb line attached at each extremity, and passing over these diagonal braces, indicated whether the instrument was level. When the wind prevented the plumb bobs from remaining stationary, a channel in the upper edge of the horizontal rod was filled with water, and if the water touched equally both extremities the level was supposed to be correct; and then the observation of the descent or elevation of the ground was made with accuracy.
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| Fig. 1. | Fig. 2. |
—Tunnelling might be classed under four general heads:
1, ancient tunnelling, to which we have just
referred; 2, modern tunnelling through soft
ground (clay deposit, &c.) and loose rock,
requiring arching; 3, modern tunnelling through
solid rock before the introduction of machinery;
4, modern tunnelling through solid rock
with the aid of machinery. The art of tunnelling
at the present day constitutes a profession
in itself, now developments succeeding each
other with great rapidity. Figs. 1 and 2 show
cross sections that may bo adopted in tunnelling:
fig. 1 through rock tenacious enough to
require no artificial support; fig. 2 where arching
may be found necessary. These examples
are from plans adopted in the construction of
the Musconetcong tunnel, New Jersey, on the
Lehigh Valley railroad extension, finished in
1875.—Tunnelling through Soft Ground.
Under the designation “soft ground,” technically
so called, the miner includes all such material
as clay, earth deposit, &c., which, if tunnelled
through, requires a temporary timber arch to
hold it in place, until the permanent brick or
stone arching is built. Loose rock, as its name
indicates, is rock either so seamy and broken
by folding or compression, or so disintegrated,
as to require an arch, generally much lighter
than those necessary in soft ground. According
to the method generally adopted in driving
a tunnel through soft ground, the first step is,
if practicable, to open out a small bottom heading
or adit, for the double purpose of draining
the ground above and making an opening
through which to carry away the material
subsequently excavated; this heading also is
required for passing in the materials used in
arching. Often, however, owing to long and
heavy cuttings necessary in the outside
approaches to a tunnel, it is deemed advisable to
begin with a top heading before the bottom
bench of the open cut is brought up to the
face of the proposed work. If a bottom heading
has been driven (and it is generally best to
do so when practicable in soft ground, while
the opposite rule holds in tunnelling through
hard rock), one of the methods of subsequent
enlarging that may be used is shown in figs. 3,
4, and 5. These represent the English plan,
so called, it being the one generally adopted
in England. For a full description of this
method of enlarging, see the “Engineering
and Mining Journal,” vol. xix., p. 392; also
Simms's “Treatise on the Blechingly and Saltwood
Tunnels.”
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| Fig. 3. | Fig. 4. |
Fig. 3 shows the bottom
heading driven, with a section excavated and
ready for arching. The enlarging and arching
of a tunnel to its full size is generally done in
lengths or sections. If there is no top heading
previously driven, 15 or 20 ft. of an
advanced heading is excavated at the top of the
proposed work (shown in figs. 3 and 4). Heavy
longitudinal bars of timber are then successively
put in, beginning with those
numbered 3, 6, and 7. The miners gradually work
down, putting in a temporary arch of timber.
When this is done, and foundations have been
dug for the succeeding masonry, the masons
take the place of the miners, and run up an
arch under the timber, which is then
withdrawn during the excavation of the next
section, and the spaces left are securely blocked
up with pieces of timber or stone. In some
methods of tunnelling, it is deemed more secure
to brick the timber in and leave it in place,
though at a considerable cost, especially when
it is necessary to bring all the heavy timber
down a shaft or slope, and through a long
distance underground. Shafts are often sunk,
and sometimes slopes, so that the work may
be attacked from several points at once.
Fig. 5.
Fig.
5 shows the arch built, and is divided into two
portions: that on the left shows the completed
tunnel, with the ballast in place and the track
laid; that on the right shows the arch in place,
and the supporting timbers struck, but still
undrawn. Where the ground is very treacherous,
and much water is encountered, an inverted
arch is often put in across the bottom of the
tunnel, to withstand the pressure from below.
Other methods are in vogue on the continent
of Europe. A description of a new system of
tunnelling by the use of iron centres, in place
of timber, devised by himself, may be found
in Ržiha's work, cited below.—Tunnelling
through Rock. One of the methods of
tunnelling through loose rock, with subsequent
timbering and arching, is shown in figs. 6 and 7;
it is the one most used in America, and is
expeditious, though probably more expensive than
the European systems.
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| Fig. 6. | Fig. 7. |
The timbers 1 and 2
are put in to support the roof and sides when
the top heading (which is generally preferred
through rock) is driven; the “legs” (2) are
occasionally braced by a bar (3), which is
supported by a raker (4), while the sides are being
dressed down when the tunnel is enlarged and
arched. The apace between the timber and
the rock above, and between the masonry and
the timber (which latter in this work should
be left in place), is packed tight with fragments
of stone, to prevent a sudden fall or stress
being brought to bear on the masonry.—Tunnelling
through solid rock by hand labor is still, in
many cases, held to be more economical than
by machinery. It is certainly so, as yet, in the
case of small tunnels through a comparatively
soft rock, where the necessary cost of a plant
of air drills and compressors would be in excess
of the economy in time gained by their use.
In driving a tunnel through rock, an advanced
heading is first driven either at bottom or top;
and this may either be of the full width of the
proposed excavation, or narrower. The heading
is always the most difficult and expensive
part of the work; for whether it be driven at
top or bottom, the miner, in removing the
remaining portion of rock, of course has much
less resistance to contend against in blasting.
Removing the top rock or the lower “bench”
is more like open-air quarrying. Longer holes
can be drilled, and heavier charges of powder
used. At the present day, however, most
heavy tunnel work is carried on with the aid
of machine drills, driven by compressed air,
which, on being liberated after acting as a
motor, serves to ventilate the work. Since
the introduction of machinery, the rate of
driving attained in tunnelling has been greatly
increased. Machine drilling was born of the
necessity for some more rapid method of
executing certain works, deemed almost too heavy
to be accomplished by ordinary means. These
were, in Europe, the Mont Cenis tunnel (see
Cenis, Mont), and in America, the Hoosac
tunnel in Massachusetts. Various types of drills
have been invented and tried abroad; among
them the Sommeiller, Dubois-François, Sachs,
Osterkamp, Brydon Davidson and Warrington,
Azolino dell' Acqua, Ferroux, McKean,
and others. Among compressors that of M.
Colladon of Geneva may be particularly noted.
At Mont Cenis the air pumps were worked by
hydraulic power. The perforators used there
were built partly from designs already
presented, but improved with original modifications
made by the engineers in charge, Messrs.
Sommeiller, Grandis, and Grattoni. A description
of the Sommeiller machines may be found
in the Portefeuille économique des machines
(1863). The Mont Cenis tunnel was begun by
hand labor in 1857, and finished in 1871, at a
total cost of about $15,000,000. The following
table, from M. Opperman's Nouvelles
annales de la construction (1869), shows the rate
of advance in that work by hand, and the
increased rate attained immediately after the
first introduction of machinery down to 1865,
working throughout with two headings:
| YEARS. | By hand, metres. |
By hand and machinery, metres. |
By machinery alone, metres. |
| 1857 | 38 | .... | ..... |
| 1858 | 459 | .... | ..... |
| 1859 | 369 | .... | ..... |
| 1860 | 343 | .... | ..... |
| 1861 | .... | 363 | ..... |
| 1862 | .... | 623 | ..... |
| 1863 | .... | .... | 802 |
| 1864 | .... | .... | 1,807 |
| 1865 | .... | .... | 1,223 |
The St. Gothard tunnel, also through the Alps,
is now (1876) in progress. From a late paper
on the subject by Daniel K. Clark, M. Inst.
C. E., London, we obtain the following general
facts concerning it. The length of the tunnel
is to be 16,295 yards or 9¼ m. The contract
prices sum up to a total estimated cost of
£1,896,945. Construction was begun in the
autumn of 1872, and the total progress
attained (two headings) up to Aug. 31, 1875,
was as follows:
| YEARS. | By hand, yards. |
By machine, yards. |
Total, yards. |
| 1872 | 182 | .... | ..... |
| 1873 | 205 | 972 | ..... |
| 1874 | .... | 1,951 | ..... |
| 1875 | .... | 1,824 | 5,084 |
The heading is driven at the top, about 8 ft.
square, dynamite being used as an explosive.
Dubois-François perforators were first used,
making an average advance of 6.63 lineal feet
a day. They were succeeded by Ferroux's,
the daily advance being raised to 10.11 ft.
Subsequently the machines of two or three
inventors, Dubois-François, McKean, and
Ferroux, were placed and worked together on
the same carriage; and it is said by M. Louis
Sautter, in an official report published in the
Revue industrielle, Aug. 18, 1875, that the
improved McKean drill has proved to be
decidedly superior to any of its competitors; its
best work on competition, with 6½
atmospheres of pressure, was a penetration of 12
in. a minute. While actually at work, its rate
will vary from 3 to 8 in. a minute, with about
800 strokes. The power is derived from water
through the agency of turbines. The cylinders
or air pumps of the compressors are 18.1 in.
in diameter, and the stroke is limited to 17¾
in., in order that the mean speed of piston may
not exceed 266 ft., or 90 revolutions a minute,
the turbine making 390 turns. The compressed
air is cooled on Dr. Colladon's system; every
piece that is in contact with the air when
undergoing compression being cooled by
currents of cold water, passed through air-tight
envelopes. It is calculated that at the present
rates of advance the St. Gothard tunnel may
be finished during the summer of 1879, or
within seven years from the date of M. Favre's
contract.—In America, both North and South,
many tunnels have been built, the modern ones
being mostly driven since the introduction of
railroads. Until the building of the Hoosac
tunnel in Massachusetts, all tunnelling through
rock in the United States was done by hand
labor, by the methods above described. The
project of tunnelling the Hoosac mountain was
broached as early as 1825. In that year a board
of commissioners, with Loammi Baldwin as
engineer, was appointed to ascertain the
practicability of making a canal from Boston to
the Hudson, in the vicinity of the junction of
the Erie canal with that river. Their report
(“Massachusetts Commissioners' Report,” 1826,
p. 141) declares that “there was no hesitation
in deciding in favor of the Deerfield and Hoosac
river route,” and that “there is no hesitation
therefore in deciding in favor of a tunnel;
but even if its expense should exceed the other
mode of passing the mountain, a tunnel is
preferable.” Railways being shortly after
introduced, the canal project was dropped. In
1828 surveys were made for three routes to
afford Massachusetts railway connection with
the west, viz., by Greenfield, by Northampton,
and by Springfield. The last or southern route
was chosen. The work was not begun
immediately, but Massachusetts never lost sight of
the advantage of a direct route to the Hudson
river. This was finally accomplished in 1842,
by the completion of the Western railroad to
Albany. In 1848 application was made for a
charter for a railroad from the terminus of
the Vermont and Massachusetts line, at or near
Greenfield, through the valley of the Deerfield
and Hoosac, to the state line, there to unite
with a railroad leading to Troy. The location
was filed in the clerk's office of Franklin
and Berkshire counties in November, 1850. In
1854 an act was passed “to enable the Troy and
Greenfield railroad company to construct the
Hoosac tunnel,” by which the state, on certain
conditions, lent its credit to the amount of
$2,000,000. The estimated cost of the proposed
double-track tunnel was $1,948,557, and of the
road and equipment $1,401,443; total, $3,350,000.
Still the company were unable to raise the
funds necessary, in addition to the state loan.
In 1855 a contract was made with E. W. Serrel
and co., under which some work was done;
and another was made with them in 1856 for
the construction of the road and tunnel for
$3,500,000, they subscribing $440,000. This
contract also fell through, as did one made
with H. Haupt and co. in the same year, by
which the railroad company agreed to pay
$3,880,000 for the completion of the road and
tunnel. In 1858 a contract was again made
with H. Haupt and co., by which the contractors
themselves agreed “to assume the labor
of collecting subscriptions and of carrying on
and completing the Troy and Greenfield railroad
and the Hoosac tunnel.” Under this
contract H. Haupt and co. were to receive
$2,000,000 in bonds of the state of Massachusetts,
to be exclusively appropriated to work done
on the tunnel; $900,000 in mortgage bonds of
the company; and $1,100,000 in cash, through
cash subscriptions and capital stock of the
company. Under this contract the work was
vigorously prosecuted up to July, 1861, when,
a difference arising between the contractors
and the state engineer, a certificate for the
amount claimed by the former on a payment
was refused, and the work was thereupon
abandoned by them. In 1862 an act passed
the Massachusetts legislature, providing “for
the more speedy completion of the Troy and
Greenfield railroad and Hoosac tunnel.”
Under this act a board of commissioners was
appointed to examine into the matter on the
part of the state. At the request of these
commissioners, the Troy and Greenfield railroad
company, acting under the authority of
certain provisions of the act, surrendered to
the commonwealth of Massachusetts, under
the several mortgages held by said
commonwealth, the road and property of the company;
such surrender having been authorized by the
board of directors, by a vote passed on Aug.
18, 1862. This action was ratified by a vote
of the stockholders, and on Sept. 4, 1862, the
commissioners took possession of the road and
its property. The commission after a full
examination made a thorough report (dated Feb.
28, 1863), embracing the three following most
valuable sub-reports: 1, a report of Charles
E. Storrow on European tunnels; 2, a report
by Benjamin H. Latrobe on the Hoosac
tunnel; 3, a report by James Laurie on the Hoosac
tunnel and the Troy and Greenfield
railroad. In conclusion the commissioners
recommended that the work should be
undertaken by the commonwealth. At this point
the cost and estimates were as follows:
| Amount advanced by the state up to the date of | |
| the commission | $1,431,447 |
| Estimated cost by the commission of completing | |
| the tunnel (double track) | 3,218,323 |
| Estimated cost of putting the road from Greenfield | |
| to the mountain in running order | 652,060 |
| Estimated cost of construction of two miles of road | |
| from western portal of tunnel to North Adams | 67,500 |
| Estimated additional cost of depot buildings, &c. | 75,000 |
| Estimated cost of rolling stock | 275,000 |
| Total estimated final cost of road and tunnel | $5,719,330 |
At this time, according to the report of James
Laurie above noted, the condition of the work
proper was as follows:
| Whole length of the proposed tunnel, feet | 24,416 | ||
| Deduct portion already excavated at each end | 2,400 | ||
| Deduct portion between shaft and proposed | |||
| western portal of tunnel | 1,850 | — | 4,250 |
| Leaving to be excavated under the mountain | 20,166 |
The shaft here referred to was on the western
slope of the mountain, 325 ft. in depth. Mr.
Laurie estimated that by sinking a central
shaft about 1,000 ft. deep and working therefrom
(which was afterward done) the tunnel,
advancing at the rates respectively of 55 ft. a
month from the two end portals, and 40 ft.
each way from the shaft, would be completed
in 11 years from date, i. e., in 1874; this
estimate being based on the supposition that the
central shaft would reach bottom in four years
from its commencement. Work was resumed
on the tunnel under the auspices of the state
in October, 1863, under the control of the
same board of commissioners, who appointed
Thomas Doane chief engineer in charge. The
governor at the same time appointed Benjamin
H. Latrobe of Baltimore state consulting
engineer of Hoosac tunnel.—Mr. Laurie in his
report to the commissioners says that shortly
after the Troy and Greenfield railroad was
chartered, the attention of inventors was turned
to the subject of tunnelling machines. One
was constructed at South Boston in 1851,
especially for the Hoosac tunnel, which weighed
about 70 tons, and was designed to cut out a
groove around the circumference of the tunnel
13 in. wide and 24 ft. in diameter, by means
of revolving cutters; the central core left was
to be subsequently blasted out with gunpowder.
It is reported to have cut, on a trial
made March 16, 1853, on a vertical face of
rock near the proposed entrance of the tunnel,
at the rate of 16½ in. an hour, and under
more favorable conditions at a previous trial
20 in. an hour. Various trials were made with
this machine, the total distance cut by it
amounting to about 10 ft., but it did not prove
successful. A second machine constructed at
Hartford, and known as the “Talbot tunnelling
machine,” also working on the principle
of revolving cutters, and adapted to cut out a
core 17 ft. in diameter, was tried about this
time near Harlem, but proved a failure. A
third machine was constructed in New York,
adapted to cut a core of 8 ft.; this was adopted
by Mr. Haupt during the continuance of
his contract, in the early days of the tunnel,
but also proved a failure. Experiments were
instituted by Mr. Haupt himself, while engaged
with his contract at Hoosac, toward the
elaboration of a percussion drill; but in 1861 the
termination of his contract for a time put an
end to them. Afterward he again took up
the subject, and in 1867 published a description
of the Haupt drill. By the time this
invention had been perfected, the Burleigh
drills, which have since attained so great a
reputation (see Blasting), had been adopted
and were in full use at Hoosac. They were
first tried in June, 1866, under the direction of
the commissioners, and even in their crude and
unimproved condition were favorably noticed
in Chief Engineer Doane's report. In January,
1867, the office of chief engineer was abolished,
and the engineer corps reduced to one resident
engineer, W. P. Granger; Mr. Latrobe still
supervising as consulting engineer. In October,
1867, owing to the accidental lighting of some
naphtha at the central shaft, the head house,
shaft buildings, &c., were consumed, and 13
lives were lost. Previous to this time portions
of the work had been let out by contract, Messrs.
Dull, Gowan, and White having the east and
central shaft headings, through rock, and Mr.
B. N. Farren the west end, through soft ground,
including the arching of the same. Owing to
the above mentioned accident, Messrs. Dull,
Gowan, and White voluntarily surrendered
their contract, received their pay, and
abandoned the work, returning it to the hands of
the commissioners. Benjamin D. Frost was
appointed superintending engineer in May,
1868, and on Dec. 24 of that year a contract
was effected between Messrs. Shanly brothers
of Montreal and the commonwealth of
Massachusetts for the final completion in full of
Hoosac tunnel. The dimensions were to be:
“in rock, unarched, 24 ft. wide and 20 ft.
high, in the clear; where arching required, 26
ft. wide and 24½ ft. high (above the rail), in
the clear.” The prices bid in the contract
varied in the different portions of the work,
and also according to whether the work was
“already begun,” “to be finished,” or for
“extension of full-sized tunnel.” The bids
accepted for the latter item were as follows:
east end section, per cubic yard, $11; central
section from shaft, $14; west end section
(part soft ground), $12; for arching part of
the tunnel with brick, per thousand of bricks
laid, $22. The total price agreed on for the
work specified by the contract was $4,594,268,
the whole to be done by March 1, 1874. At
this time Mr. Latrobe resigned as consulting
engineer; and that post, after the successive
resignations of James Laurie and Edward S.
Philbrick of Boston, is now (1876) held by
Thomas Doane. The work was vigorously
attacked by the Messrs. Shanly at all points.
The Burleigh drills and compressors were used
throughout their contract with excellent
results. Under their patronage, the manufacture
of nitro-glycerine (previously used in the
tunnel) was carried on and improved by George M.
Mowbray of North Adams. The east heading
met the one driven east from the central shaft
on Dec. 12, 1872; the west heading met the
one driven west from the shaft on Nov. 27,
1873; the errors in alignment and levels were
astonishingly small, especially as the former
meeting was at a distance of 1,563 ft., the latter
of 2,056 ft., from the shaft, down which the
plumb lines had to be carried over 1,000 ft.
The Messrs. Shanly concluded their contract and
effected a final settlement Dec. 22, 1874.
Independently of the contract taken by them, an
agreement was entered into between the state
and B. N. Farren, on Nov. 19, 1874, to do
certain arching and enlarging at the eastern portal
of the tunnel. By authority of an act passed
by the legislature in 1874, a commission of
experts, comprising Prof. T. Sterry Hunt of Boston
and Prof. James Hall of Albany as geologists,
and Thomas Doane, Josiah Brown, and Daniel
L. Harris as civil engineers, was appointed to
examine and report on the amount of arching
that would be still necessary. Their reports
are embodied in that of the commission of
1875, as is also a report from Edward S.
Philbrick, consulting engineer, recommending an
additional amount of 1,600 ft. of arching,
besides that included in the Shanly contract.
Work on this arching is still (March, 1876) in
progress. Under a law of 1874 a board of
corporators of the Boston, Hoosac Tunnel, and
Western railroad was created, who reported
that the tunnel had up to that time cost the
state about $14,000,000. By a subsequent act
of 1874 the corporators were superseded by
five directors, to whom the interest of the state
in the tunnel and railroad was transferred.—The
next tunnel in the United States in which
machine drills were introduced with effect,
after their practicability had been
demonstrated at Hoosac, was the Nesquehoning tunnel
in Pennsylvania, constructed under the
direction of J. Dutton Steele as chief engineer.
(See paper by J. Dutton Steele in “Transactions
of the American Society of Civil
Engineers,” 1871.) Here the Burleigh drill and
ordinary black powder were used. The
Musconetcong tunnel, on the Lehigh Valley railroad
extension through New Jersey, was the
next heavy piece of work in the eastern states
on which machine drilling was adopted. This
tunnel was begun in April, 1872, and finished
in June, 1875, under the charge of Robert H.
Sayre, chief engineer and general superintendent
of the Lehigh Valley railroad company.
Charles McFadden of Philadelphia took the
contract, and completed what has been
conceded to be one of the heaviest pieces of tunnel
work ever attempted in America, and yet
one of the most rapidly built. Every modern
appliance was used. The Ingersoll drill was
adopted, about 26 being kept on hand, and from
16 to 18 in constant use. Four Burleigh
compressors supplied the air required at the west
end, and four Rand and Waring compressors at
the east. Dynamite was used throughout as an
explosive, and gave entire satisfaction. Very
heavy difficulties were encountered in the
prosecution of the work, owing to the large bodies
of water met with. The total length of the
tunnel was a little less than one mile. It was
begun by sinking a slope to grade on the western
side of the mountain, about one third of
the distance through, virtually dividing the
tunnel into one third of soft ground working
at the west, and two thirds of very hard ground
at the east. The headings were started east
and west from the bottom of this slope in
November, 1872. The east heading had been
started in July, 1872. Owing to the heavy
cutting necessary at the west end, the heading
could not be connected with those from
the slope, and from a shaft subsequently sunk,
until November, 1873. In May, 1873, so
heavy a body of water was struck in the slope
heading going east, that it could not be
controlled. The miners were driven out, and the
slope half filled. The water undermining the
props and backing of the timbering in the
slope, part of the roof fell in, and the work
at that point had to be abandoned temporarily.
A shaft was then sunk west of the slope, and
headings were driven east and west to tap and
draw off this water. Here again new and
even heavier bodies of water were encountered,
resulting in great expense and much
loss of time. Finally the difficulties were
overcome, the water tapped, and work
resumed on the original slope heading going
east, which met the east heading coming west
in December, 1874, the errors in alignment
and level being less than half an inch. (For
further details on the construction of this tunnel
see a paper by Henry S. Drinker in the
“Transactions of the American Institute of
Mining Engineers,” vol. iii.) With the admirable
and delicate instruments now so readily
obtainable, it would require a positive effort of
carelessness on the part of the engineer to
entail any serious error in tunnel surveys.
Especially noticeable among instruments are those
recently perfected by Messrs. Heller and
Brightly of Philadelphia, who have made a specialty
of tunnel transits.—The above described three
tunnels have been taken as particular
examples, because they are the latest driven at
the present time (March, 1876), and are the
best examples of the present stage of the art
of tunnelling in the United States. A large
tunnel in Nevada, known as the Sutro tunnel,
has been in process of construction with
machinery for some years. (See Nevada.) It
is intended to serve as an adit to the
Comstock lode. (See “Report of United States
Sutro Tunnel Commission,” Washington, Jan.
6, 1872.)—One of the first tunnels in the United
States was on the Alleghany Portage railroad
in Pennsylvania. It was built in 1831,
double track, 900 ft. long; contract price, $1 47
per cubic yard; total cost, 14,857 cubic yards,
$21,840. Another early work was the Black
Rock tunnel, on the Reading railroad, built in
1836. This was 1,932 ft. long, and the
excavation proper of the tunnel cost $125,935.
According to data furnished by Mr. B. H.
Latrobe of Baltimore, there are 44 tunnels on
the line of the Baltimore and Ohio railroad
and its branches, with an aggregate length of
37,861 ft., or 7 m. 901 ft., the tunnels varying
from 80 to 4,100 ft. in length. The Sand Patch
tunnel, on the Pittsburgh and Connellsville
branch, was begun in 1854 and finished in 1871.
The work during this time was intermitted
for a total period of nine years, owing chiefly
to the financial embarrassments of 1858. It
was driven through the old red sandstone, and
cost nearly $500,000. The Kingwood tunnel,
4,100 ft. long, was begun in September, 1849,
and finished in May, 1852, at a total cost,
including excavation and arching, of $724,000.
The Broadtree tunnel, 2,350 ft. long, on the
same road, begun in the spring of 1851, was
completed in April, 1853, at a total cost
(excavation and arching) of $503,000. The Chesapeake
and Ohio railroad is 423 m. long, and
has 7 m. of tunnelling; the Big Bend tunnel,
on the Greenbrier division, is 6,400 ft. long.—Of
the rates of progress attainable by
machine drilling, a fair average can be deduced
from three large tunnels driven through
different kinds of rock. At the Hoosac tunnel,
through mica schist and micaceous gneiss, with
nitro-glycerine, the progress attained by Shanly
brothers at the east end in 1869 averaged
139½ ft. a month, and in 1870, 126½ ft.; at the
west end in 1870, 100¼ ft. In sinking the
central shaft 1,080 ft. in depth, through rock, the
average total progress per working month was
21 ft., but the 230 ft. sunk by Shanly brothers
was driven in 7½ working months, or at the rate
of 30.7 ft. a month. At Nesquehoning, through
conglomerate, the average attained in 12
months' driving was 100 ft. a month; while
through red shale an experience of two months
gave an average of 160 ft. a month. Common
black powder was used, the consumption in
the conglomerate being about 6 lbs., and in red
shale 3½ lbs. per cubic yard of rock broken. At
the Musconetcong tunnel the average monthly
advance through a very hard syenitic gneiss,
pronounced harder by experts familiar with
both than any body of rock met in the Hoosac
tunnel, was in 1874: east heading, average of
12 months, 115.8 ft.; west heading, average
of last 6½ months, when steady work was
attained, 136.8 ft. At this tunnel a shaft was
also driven 110 ft. in depth through soft ground,
with timbering, at an average rate of 24¼ ft. a
month. The prices bid at the present day for
tunnel excavation vary from $4 to $7 and $8
per cubic yard. But the contract prices are not
always a sure criterion as to the final cost; $6
per cubic yard is a medium bid. Very heavy
and expensive tunnel work is often done in
constructing underground railways through cities.
In these the plan generally adopted is first
to make an open-air excavation through the
streets, then build the arches and fill in the
ground again. A very heavy tunnel was lately
finished under the London docks, passing also
under some large warehouses, and needing very
careful work. The quantity of water pumped
was enormous. The final cost was at the
rate of £390,000 a mile.—Subaqueous Tunnels.
Among these should be particularly noted the
first one built under the Thames at London.
Except however in view of its vast expense,
and the fact that it was the forerunner of modern
subaqueous tunnelling, its record at the
present day, since the system has been further
developed, has no very practical interest. It
was begun in 1807, intermitted, and resumed
in 1825, under Sir M. I. Brunel, intermitted
again, and at last completed and opened for
foot passengers in 1843. Its total length is
1,200ft.; final cost nearly £1,200 per lineal
yard advanced. (See London, vol. x., pp.
616-617.)—A tunnel that has attracted much
attention throughout both Europe and this
country is the one at Chicago, driven out
under Lake Michigan, for the purpose of obtaining
pure water for the city. This tunnel, begun
in March, 1864, and completed in March, 1867,
was entirely original in plan; the engineer
was Mr. E. S. Chesbrough. A crib was first
sunk in Lake Michigan, about two miles from
the shore, 58 ft. in horizontal outside measurement
on each of the five sides, and 40 ft. high.
The inner portion or well has sides parallel
with the outer ones, 22 ft. long each, leaving
the distance between the inner and outer faces
of the crib, or thickness of the breakwater, 25
ft. This breakwater was built on a flooring of
12-inch white pine timber, laid close together.
The outer and inner vertical faces, and the
middle wall between them, were all of solid
12-inch white pine timber, except the upper
10 ft. of the outside, which was of white oak,
to withstand better the action of the ice. The
outer and inner walls were strengthened and
connected with brace walls and cross ties of
12-inch timbers, all securely bolted. The crib
was built on land, launched, towed into place,
filled with atone, and sunk. An iron cylinder,
cast in 9-foot sections, of 9 ft. internal diameter
and 2¼ in. thick, was then lowered within
the crib to the bottom of the lake; and this
cylinder was connected with the land two miles
distant by a tunnel under the lake bottom.
Gate wells were constructed in the sides of the
crib, and after the completion of the tunnel
the top section of the cylinder, extending above
water level, was removed, and the water
admitted through a screen. The tunnel, of
circular cross section, was driven through a stiff
blue clay; diameter of excavation 5 ft.,
subsequently lined with two rings of brick. The
final cost in full to the city was $457,844.
According to the statements and books of the
contractors, the items were: crib and outer
shaft, $117,500; land shaft, $12,000; tunnel
proper, $195,000; total, $324,000. The balance
of the expenditure was used in necessary
contingencies. For full details of this work see
“Eighth Annual Eeport of the Board of Public
Works” (Chicago, 1869); also a report of
Prof. W. P. Blake, commissioner of California
to the Paris exposition (1867). A second tunnel,
7 ft. in diameter, extending to the same
crib, was completed in July, 1874, at a total cost
of $411,510; and two tunnels for traffic have
been constructed under Chicago river. A tunnel
under Lake Erie, at Cleveland, Ohio,
begun in August, 1869, finished in March, 1874,
is similar in plan, purpose, and construction
to the one first driven under the lake at
Chicago, except that much greater difficulties were
encountered in its construction, from meeting
several bodies of very soft ground. It is
6,606 ft. in length, and the total cost amounted
to $320,352.—It was estimated by Capt. Tyler
in 1873 that between 300,000 and 400,000
persons yearly crossed the English channel at
Dover, that the number was constantly increasing,
and that if a tunnel were built it would
probably be doubled. The idea of a tunnel
under the channel was first broached by M.
Mathieu, a French engineer, who laid plans
for one before Bonaparte in 1802. Owing to
the subsequent disturbances the projector and
his plans were lost sight of. Subsequently
plans were proposed by M. Thomé de Gamond,
Dr. Payerne, Messrs. Franchot and Tessier,
Favre, Mayer, Dunn, Austin, Sankey, Boutet,
Hawkins Simpson, Low, Boydon, Brunlees,
Waenmaker, and others. To M. Thomé de
Gamond is conceded the credit of pushing the
project to its present advancement. In 1872
the present channel company was incorporated,
Sir John Hawkshaw, Mr. James Brunlees, and
M. Thomé de Gamond being appointed the
engineers. The route finally adopted places the
tunnel on a line drawn from St. Margaret's bay
near the South Foreland, on the English side, to
a point between Sangatte and Calais in France.
The total proposed length of the tunnel is 31
m., of which 22 m. will be under the channel.
Should the preliminary tests prove favorable,
it is proposed to begin the actual construction
by sinking shafts on either shore to the depth
of 450 ft. below high-water mark. Driftways
will be driven from the bottom of these for
the drainage of the subsequent tunnel proper.
The tunnel, if constructed, is to begin 200 ft.
above the driftway, and will be driven from
both ends. It is to be through the chalk, and
in no part of it will there be less than 200 ft.
of ground between the crown of the arch and
the bed of the channel. It will be on a down
grade of one foot in 80 to the junction of the
drainage driftway, and then on an up grade
of one in 2,640 to the middle of the strait. It
is proposed to drive the driftway or heading
with Dickinson Brunton's machine for tunnelling
through chalk, which works like an auger
boring wood. It is believed, from actual work
done, that this machine will advance at the
rate of from a yard to a yard and a quarter an
hour. At this rate it would require two years
to construct the driftway, driving from either
end, at an estimated cost of £800,000. After
the heading has been driven through, it has
been estimated that four years' time and an
outlay of £4,000,000 will finish the work,
including arching; but Sir John Hawkshaw and
his associates consider it best, before beginning
the work, to double this figure as an
estimate. The preliminary works to be undertaken
are the sinking of two shafts at either
extremity of the tunnel, from which an ordinary
mining driftway is to be driven about
half a mile out under the sea, the cost of which
is estimated at £160,000. This done, the engineers
will be better able to judge of the ultimate
practicability of the work.—See Lehrbuch
der gesammten Tunnelbaukunst, by F. Ržiha (6
vols., Berlin, 1865-'72); and Der Tunnelbau,
by J. G. Schön (4to, Vienna, 1866). There is
no complete work in English on modern
tunnelling. The facts in this article are largely
drawn from a practical treatise on American
and European tunnelling, now (1876) in course
of preparation by Henry S. Drinker, E. M., of
Philadelphia.