Shenandoah herald. [volume] (Woodstock, Va.) 1865-1974, 1873-11-06

1t passes rather to the west of thai
mountain, upon more practicable lin.
for engineering operations.
| When operations began, the rock
was pierced with hand drills, and TIL
masses were blasted out with power
This was continued by the italian
workmen until 1861, and by the French
until 1861; but the progress made was
SO exceedingly small that fifty years
would have been consumed in COM
lpleting the work. 1t was necessary,
| therefore, to devise some machinery
which would remove the rock in a more
expeditions manner. It was, of course,
impossible to use steam, because fires
could not be tolerated in the tunnel.
and the steam, if made outside, would
condense before it reached the drills at
| the scene of action. After much ex-
perimenting, a machine was invented
which worked the drills with compress
ed air. At the entrances to the tunnel
apparatus was erected which was
operated by the streams that came
tumbling down the mountain side. The
air was compressed in cylinders, and
conducted far into the excavation in
strong and heavy rubber hose. The
drilling apparatus was machine which
carried large number of borers, each
of which cut q separate hole in the rock
Each drill moved to and fro in a
cylinder, and when the compressed air
was admitted, the drill was driven
against the rock with force of nearly
two hundred pounds, turned partially
around and withdrawn. In this
manner two hundred blows minute
were given by each perforator, and
when the holes were of the required
depth the drills were withdrawn and
blasting operations began Powder
was not used when the work was well
under way; nitroglycerine was found
less troublesome and more effective
Another excellent result of the use
Of compressed air was, that the work
man always had plenty Of pure outside
air to breathe. That which was dis
charged from the drills was more than
sufficient to supply all who were en-
gagged in work A man can live at
ease during twenty four hours with ten
cubic metres of air, and the air-pumps
gave to each of the workman forty one
cubic metres, or more than four times
as much as was wanted, so that they
were actually better off under the
mountain than outside of it.
The friction Of the process of CON-
preston heated the air slightly, and the
work was conducted in a temperature
of about seventy degrees Fahrenheit,
even when the outside temperature was
below freezing point. The workmen
had to dress lightly in the tunnel in the
cold season, and to exercise great care
in coming out. In each twenty four
hours Sc, 400 cubic metres of air were
introduced into the tunnel by the rub
Der tubes. Machinery Of the same kind
were used with excellent effect in
a railroad tunnel near Mauch Chunk,
in this State, three OF four yea rs
ago, and it is possible that many of my
readers have seen it in operation.
The Mont Gents tunnel runs through
various kinds of rock, las limestone, schist
and quartz. At the Italian end nothing
but schist was found, and it was cut
away at the rate of five feet day. On
the Savoy side the schist extended for
nearly twenty-five hundred yards, and
was succeeded by five hundred and fit
ty yards Of quartz, and over three thou
sand yards of limestone. The drills
went through the schist at the rate OF
four feet per day, through the quartz
at the rate Of two feet, and the limestone
was excayated at the rate of six feet a
day. The lining wall was built at each
end as fast as the drilling machines ad
vanced. The entrances to the tunnel
are twenty-five feet in height and as
many in width. At Forneaux, the vault
is in the centre; at Bardoneche, it is ell
liptic, with height of a foot or more
than at Forneaux, in consequence of the
excess OF pressure, owing to the fact
that the qualification of the rock is al
most horizontal. The lining walls are
OF stone, and they have thickness var
ying from two to three feet, according
to the weight of the earth.
There is difference between the
height OF the entrances of nearly five
hundred feet. At Forneaux, the eleva-
ton Of the mouth of the tunnel is 3,946
above the sea level; at Bardoneche, it is
1881 feet above. To provide against
a possible rush of water, which was an
ticipated, the tunnel was constructed
with rising gradient of in 1000 from
the Bardoneche side; from Fourneaux
to the middle ofthe tunnel the gradient
is 22.2 per thousand, OF l in AS
/ The distance through the tunnel is
miles 1920 yards. At the time of the