It was possible in the model series, without neglecting any major
advancement in the art of rock tunneling, to complete the sequence of
development with only a single additional model. Many of the greatest
works of civil engineering have been those concerned directly with
transport, and hence are the product of the present era, beginning in
the early 19th century. The development of the ancient arts of route
location, bridge construction, and tunnel driving received a powerful
stimulation after 1800 under the impetus of the modern canal, highway,
and, especially, the railroad.
The Hoosac Tunnel, driven through Hoosac Mountain in the very
northwest corner of Massachusetts between 1851 and 1875, was the first
major tunneling work in the United States. Its importance is due not
so much to this as to its being literally the fountainhead of modern
rock-tunneling technology. The remarkable thing is that the work was
begun using methods of driving almost unchanged during centuries
previous, and was completed twenty years later by techniques which
were, for the day, almost totally mechanized. The basic pattern of
operation set at Hoosac, using pneumatic rock drills and efficient
explosives, remains practically unchanged today.
The general history of the Hoosac project is so thoroughly recorded
that the briefest outline of its political aspects will suffice here.
Hoosac Mountain was the chief obstacle in the path of a railroad
projected between Greenfield, Massachusetts, and Troy, New York.
The line was launched by a group of Boston merchants to provide a
direct route to the rapidly developing West, in competition with the
coastal routes via New York. The only route economically reasonable
included a tunnel of nearly five miles through the mountain--a
length absolutely without precedent, and an immense undertaking in
view of the relatively primitive rock-working methods then available.
[Illustration: Figure 5.--BURLEIGH ROCK DRILL, improved model of about
1870, mounted on frame for surface work. (Catalog and price list: The
Burleigh Rock Drill Company, 1876.)]
The bore's great length and the desire for rapid exploitation inspired
innovation from the outset of the work. The earliest attempts at
mechanization, although ineffectual and without influence on tunnel
engineering until many years later, are of interest. These took the
form of several experimental machines of the "full area" type,
intended to excavate the entire face of the work in a single operation
by cutting one or more concentric grooves in the rock. The rock
remaining between the grooves was to be blasted out. The first such
machine tested succeeded in boring a 24-foot diameter opening for 10
feet before its total failure. Several later machines proved of equal
merit.[2] It was the Baltimore and Ohio's eminent chief engineer,
Benjamin H. Latrobe, who in his _Report on the Hoosac Tunnel_
(Baltimore, Oct. 1, 1862, p. 125) stated that such apparatus contained
in its own structure the elements of failure, "... as they require
the machines to do too much and the powder too little of the work,
thus contradicting the fundamental principles upon which all
labor-saving machinery is framed ... I could only look upon it as a
misapplication of mechanical genius."
[Illustration: Figure 6.--HOOSAC TUNNEL. Flash-powder photograph of
Burleigh drills at the working face. (_Photo courtesy of State
Library, Commonwealth of Massachusetts._)]
Latrobe stated the basic philosophy of rock-tunnel work. No mechanical
agent has ever been able to improve upon the efficiency of explosives
for the shattering of rock. For this reason, the logical application
of machinery to tunneling was not in replacing or altering the
fundamental process itself, but in enabling it to be conducted with
greater speed by mechanically drilling the blasting holes to receive
the explosive.
Actual work on the Hoosac Tunnel began at both ends of the tunnel in
about 1854, but without much useful effect until 1858 when a contract
was let to the renowned civil engineer and railroad builder, Herman
Haupt of Philadelphia. Haupt immediately resumed investigations of
improved tunneling methods, both full-area machines and mechanical
rock drills. At this time mechanical rock-drill technology was in a
state beyond, but not far beyond, initial experimentation. There
existed one workable American machine, the Fowle drill, invented in
1851. It was steam-driven, and had been used in quarry work, although
apparently not to any commercial extent. However, it was far too
large and cumbersome to find any possible application in tunneling.
Nevertheless, it contained in its operating principle, the seed of a
practical rock drill in that the drill rod was attached directly to
and reciprocated by a double-acting steam piston. A point of great
importance was the independence of its operation on gravity,
permitting drilling in any direction.
While experimenting, Haupt drove the work onward by the classical
methods, shown in the left-hand section of the model (fig. 2). At
the far right an advance heading or adit is being formed by pick and
hammer work; this is then deepened into a top heading with enough
height to permit hammer drilling, actually the basic tunneling
operation. A team is shown "double jacking," i.e., using two-handed
hammers, the steel held by a third man. This was the most efficient of
the several hand-drilling methods. The top-heading plan was followed
so that the bulk of the rock could be removed in the form of a bottom
bench, and the majority of drilling would be downward, obviously the
most effective direction. Blasting was with black powder and its
commercial variants. Some liberty was taken in depicting these steps
so that both operations might be shown within the scope of the model:
in practice the heading was kept between 400 and 600 feet in advance
of the bench so that heading blasts would not interfere with the bench
work. The bench carriage simply facilitated handling of the blasted
rock. It was rolled back during blasts.
[Illustration: Figure 7.--HOOSAC TUNNEL. GROUP OF MINERS descending
the west shaft with a Burleigh drill. (_Photo courtesy of State
Library, Commonwealth of Massachusetts._)]
The experiments conducted by Haupt with machine drills produced no
immediate useful results. A drill designed by Haupt and his associate,
Stuart Gwynn, in 1858 bored hard granite at the rate of 5/8 inch per
minute, but was not substantial enough to bear up in service. Haupt
left the work in 1861, victim of intense political pressures and
totally unjust accusations of corruption and mismanagement. The
work was suspended until taken over by a state commission in 1862.
Despite frightful ineptitude and very real corruption, this period
was exceedingly important in the long history both of Hoosac Tunnel
and of rock tunneling in general.
The merely routine criticism of the project had by this time become
violent due to the inordinate length of time already elapsed and the
immense cost, compared to the small portion of work completed. This
served to generate in the commission a strong sense of urgency to
hurry the project along. Charles S. Storrow, a competent engineer, was
sent to Europe to report on the progress of tunneling there, and in
particular on mechanization at the Mont Cenis Tunnel then under
construction between France and Italy. Germain Sommeiller, its chief
engineer, had, after experimentation similar to Haupt's, invented a
reasonably efficient drilling machine which had gone into service at
Mont Cenis in March 1861. It was a distinct improvement over hand
drilling, almost doubling the drilling rate, but was complex and
highly unreliable. Two hundred drills were required to keep 16 drills
at work. But the vital point in this was the fact that Sommeiller
drove his drills not with steam, but air, compressed at the tunnel
portals and piped to the work face. It was this single factor, one of
application rather than invention, that made the mechanical drill
feasible for tunneling.
All previous effort in the field of machine drilling, on both sides
of the Atlantic, had been directed toward steam as the motive power.
In deep tunnels, with ventilation already an inherent problem, the
exhaust of a steam drill into the atmosphere was inadmissible.
Further, steam could not be piped over great distances due to serious
losses of energy from radiation of heat, and condensation. Steam
generation within the tunnel itself was obviously out of the question.
It was the combination of a practical drill, and the parallel
invention by Sommeiller of a practical air compressor that resulted in
the first workable application of machine rock drilling to tunneling.
[Illustration: Figures 8 & 9.--HOOSAC TUNNEL. CONTEMPORARY
ENGRAVINGS. As such large general areas could not be sufficiently
illuminated for photography, the Museum model was based primarily on
artists' versions of the work. (_Science Record_, 1872; _Leslie's
Weekly_, 1873.)]
The Sommeiller drills greatly impressed Storrow, and his report of
November 1862 strongly favored their adoption at Hoosac. It is curious
however, that not a single one was brought to the U.S., even on trial.
Storrow does speak of Sommeiller's intent to keep the details of the
machine to himself until it had been further improved, with a view to
its eventual exploitation. The fact is, that although workable, the
Sommeiller drill proved to be a dead end in rock-drill development
because of its many basic deficiencies. It did exert the indirect
influence of inspiration which, coupled with a pressing need for
haste, led to renewed trials of drilling machinery at Hoosac. Thomas
Doane, chief engineer under the state commission, carried this program
forth with intensity, seeking and encouraging inventors, and himself
working on the problem. The pattern of the Sommeiller drill was
generally followed; that is, the drill was designed as a separate,
relatively light mechanical element, adapted for transportation by
several miners, and attachable to a movable frame or carriage during
operation. Air was of course the presumed power. To be effective, it
was necessary that a drill automatically feed the drill rod as the
hole deepened, and also rotate the rod automatically to maintain a
round, smooth hole. Extreme durability was essential, and usually
proved the source of a machine's failure. The combination of these
characteristics into a machine capable of driving the drill rod into
the rock with great force, perhaps five times per second, was a
severe test of ingenuity and materials. Doane in 1864 had three
different experimental drills in hand, as well as various steam
and water-powered compressors.
Success finally came in 1865 with the invention of a drill by Charles
Burleigh, a mechanical engineer at the well-known Putnam Machine Works
of Fitchburg, Massachusetts. The drills were first applied in the east
heading in June of 1866. Although working well, their initial success
was limited by lack of reliability and a resulting high expense for
repairs. They were described as having "several weakest points." In
November, these drills were replaced by an improved Burleigh drill
which was used with total success to the end of the work. The era of
modern rock tunneling was thus launched by Sommeiller's insight in
initially applying pneumatic power to a machine drill, by Doane's
persistence in searching for a thoroughly practical drill, and by
Burleigh's mechanical talent in producing one. The desperate need to
complete the Hoosac Tunnel may reasonably be considered the greatest
single spur to the development of a successful drill.
The significance of this invention was far reaching. Burleigh's was
the first practical mechanical rock drill in America and, in view of
its dependability, efficiency, and simplicity when compared to the
Sommeiller drill, perhaps in the world. The Burleigh drill achieved
success almost immediately. It was placed in production by Putnam for
the Burleigh Rock Drill Company before completion of Hoosac in 1876,
and its use spread throughout the western mining regions and other
tunnel works. For a major invention, its adoption was, in relative
terms, instantaneous. It was the prototype of all succeeding
piston-type drills, which came to be known generically as "burleighs,"
regardless of manufacture. Walter Shanley, the Canadian contractor who
ultimately completed the Hoosac, reported in 1870, after the drills
had been in service for a sufficient time that the techniques for
their most efficient use were fully understood and effectively
applied, that the Burleigh drills saved about half the drilling costs
over hand drilling. The per-inch cost of machine drilling averaged 5.5
cents, all inclusive, vs. 11.2 cents for handwork. The more important
point, that of speed, is shown by the reports of average monthly
progress of the tunnel itself, before and after use of the air drills.
_Year_ _Average monthly
progress in feet_
1865 55
1866 48
1867 99
1868 --
1869 138
1870 126
1871 145
1872 124
[Illustration: Figure 10.--TRINITROGLYCERINE BLAST at Hoosac Tunnel.
(_Leslie's Weekly_, 1873.)]
The right portion of the model (fig. 3) represents the workings during
the final period. The bottom heading system was generally used after
the Burleigh drills had been introduced. Four to six drills were
mounted on a carriage designed by Doane. These drove the holes for
the first blast in the center of the heading in about six hours. The
full width of the heading, the 24-foot width of the tunnel, was then
drilled and blasted out in two more stages. As in the early section,
the benches to the rear were later removed to the full-tunnel height
of about 20 feet. This operation is shown by a single drill (fig. 4)
mounted on a screw column. Three 8-hour shifts carried the work
forward: drilling occupied half the time and half was spent in running
the carriage back, blasting, and mucking (clearing the broken rock).
[Illustration: Figure 11.--HOOSAC TUNNEL survey crew at engineering
office. The highest accuracy of the aboveground and underground survey
work was required to insure proper vertical and horizontal alignment
and meeting of the several separately driven sections. (_Photo
courtesy of State Library, Commonwealth of Massachusetts._)]
The tunnel's 1028-foot central shaft, completed under the Shanley
contract in 1870 to provide two additional work faces as well as a
ventilation shaft is shown at the far right side of this half of the
model. Completed so near the end of the project, only 15 percent of
the tunnel was driven from the shaft.
The enormous increase in rate of progress was not due entirely to
machine drilling. From the outset of his jurisdiction, Doane undertook
experiments with explosives as well as drills, seeking an agent more
effective than black powder. In this case, the need for speed was not
the sole stimulus. As the east and west headings advanced further and
further from the portals, the problem of ventilation grew more acute,
and it became increasingly difficult to exhaust the toxic fumes
produced by the black powder blasts.
In 1866, Doane imported from Europe a sample of trinitroglycerine,
the liquid explosive newly introduced by Nobel, known in Europe as
"glonoïn oil" and in the United States as "nitroglycerine." It already
had acquired a fearsome reputation from its tendency to decompose with
heat and age and to explode with or without the slightest provocation.
Nevertheless, its tremendous power and characteristic of almost
complete smokelessness led Doane to employ the chemist George W.
Mowbray, who had blasted for Drake in the Pennsylvania oil fields, to
develop techniques for the bulk manufacture of the new agent and for
its safe employment in the tunnel.
Mowbray established a works on the mountain and shortly developed
a completely new blasting practice based on the explosive. Its
stability was greatly increased by maintaining absolute purity in the
manufacturing process. Freezing the liquid to reduce its sensitivity
during transport to the headings, and extreme caution in its handling
further reduced the hazard of its use. At the heading, the liquid was
poured into cylindrical cartridges for placement in the holes. As with
the Burleigh drill, the general adoption of nitroglycerine was
immediate once its qualities had been demonstrated. The effect on the
work was notable. Its explosive characteristics permitted fewer blast
holes over a given frontal area of working face, and at the same time
it was capable of effectively blowing from a deeper drill hole, 42
inches against 30 inches for black powder, so that under ideal
conditions 40 percent more tunnel length was advanced per cycle of
operations. A new fuse and a system of electric ignition were
developed which permitted simultaneous detonation and resulted
in a degree of effectiveness impossible with the powder train and
cord fusing used with the black powder. Over a million pounds of
nitroglycerine were produced by Mowbray between 1866 and completion
of the tunnel.
[Illustration: Figure 12.--WORKS AT THE CENTRAL SHAFT, HOOSAC TUNNEL,
for hoisting, pumping and air compressing machinery, and general
repair, 1871. (_Photo courtesy of State Library, Commonwealth of
Massachusetts._)]
[Illustration: Figure 13.--HOOSAC TUNNEL. AIR-COMPRESSOR BUILDING on
Hoosac River near North Adams. The compressors were driven partially
by waterpower, derived from the river. (_Photo courtesy of State
Library, Commonwealth of Massachusetts._)]
[Illustration: Figure 14.--WEST PORTAL OF HOOSAC TUNNEL before
completion, 1868, showing six rings of lining brick. (_Photo
courtesy of State Library, Commonwealth of Massachusetts._)]
When the Shanleys took the work over in 1868, following political
difficulties attending operation by the State, the period of
experimentation was over. The tunnel was being advanced by totally
modern methods, and to the present day the overall concepts have
remained fundamentally unaltered: the Burleigh piston drill has been
replaced by the lighter hammer drill; the Doane drill carriage by the
more flexible "jumbo"; nitroglycerine by its more stable descendant
dynamite and its alternatives; and static-electric blasting machines
by more dependable magnetoelectric. But these are all in the nature of
improvements, not innovations.
Unlike the preceding model, there was good documentation for this one.
Also, the Hoosac was apparently the first American tunnel to be well
recorded photographically. Early flashlight views exist of the drills
working at the heading (fig. 6) as well as of the portals, the winding
and pumping works at the central shaft, and much of the machinery and
associated aspects of the project. These and copies of drawings of
much of Doane's experimental apparatus, a rare technological record,
are preserved at the Massachusetts State Library.