Burlington weekly free press. [volume] (Burlington, Vt.) 1866-1928, 1883-08-17
TIE HUDSON RIVER TUNNEL.

Now that the great Brooklyn Bridge has
been completed and opened to the public, |
and the newspapers have ceased talking about |
the eighth wonder of the world, it may be in
place to call attention to II work not less
daring in conception and wonderful in exc
cution, though concealed from the eye Of
the multitude - the great Hudson river
tunnel, nowin process OF construction. This
remarkable effort of modern engineering
science, if successfully carried out, bids fair
to equal, II not surpass, in interest and
value the triumph of RoeGlng. It's difficult
ties, probably, are nearly twice as great us
those which have been met and overcome in
the construction of the Brooklyn Bridge
The tunnel is to be double, the two passages
running parallel, about twenty-five feet
apart, with connections at intervals of about
one thousand feet. Nearly oachalf mile OF
tunnel has already been completed, but the
width of the river at the point chosen
is such that the distance between the ,bulli
he DIS will be some 8, 400 feet, and between
the cassons n little over one mile, exclusive of
the approaches. Work on the tunnel is, at
present, temporarily suspended. Extreme
difficulties have been met, but have been 50
far overcome as to warrant continuance
of the work in a short timc-probably by
the first of October.
Before describing the tuunel and its me-
thod of construction it might be well to state,
briefly, Il few of the principal difficulties
which stand in the way of its completion.
In the first place, the bed of the Hudson
river at this point is composed of "slt,"
substance which previous experience in tun
neling has proved extremely uniavorablc to
this branch of engineering One of the chief
dangers is that arising from the tremendous
pressure cxerted by the continuous
lateral movement of large body
of silt. The vertical pressure of the silt can
be mechanically computed, but the hori-
zontal pressure is entirely variable. Auoth-
err ditllcultyand danger arises from the liza
bility of the iron roof-pating, by which the
extension of the tunnel is at present pro-
tected, to fall in on the working section, and
admit the water. This has occurred once
already, but, we believe, without loss of
life. The bulkhead was restored by the aid
of workmen clad in diving costume There
arc other minor.diilicultes which are con-
stan,ly arising bnt, so far, all have been
successfully met, and it is probable that any
others, now unknown will be overcome by
the same perseverance and scientific skill
already displayed.
The tunnel is being constructed by what
Is known as the pneumatic process" which
may be illustrated by tumbcr held bottom
up in the water. The air in the tumber
will displace a certain portion of water, so
as to leave space untitled by the
latter. In like manner huge caisson
was first sunk, its sides made sohd
with timber, and its top tightly closed,
and fitted with pipe through which enough
air was pumped into the caisson to keep out
all water from the connected tunnel, when
below the water line. AT the proper point
the caisson was chselled through, and the
tunnel commenced in a lateral direction
The walls of the tunnel are fortified as they
progress, with plates of boiler iron and an in.
ner wall Oh DTlCk anu mortar. he work oil
tunneling has been begun on both the New
York and New Jersey sides of the river. The
tunnel is being built In sections of ten feet in
length each, protected at the ends by nova
bic iron bulkheads. The bukhead is ad-
vanced from end to end of each section us
the work advances The water which pcr
colates through the soil would naturally rise
till its level was reached and I'll the tunnel.
were it not that Ivy increasing the a,mospher-
ic pressure within the caisson or tunnel by
artificial means it is kept down. The safety
OF the workmen can only be secured by rem
dering the tunnel air tight, or Yearly so, that
it may hold the air which is forced in for the
purpose of keeping the water down to II
proper level. The theory of The engineers
is that the earth in front of the side Of the
caisson or Of the iron bulkhead, when that is
used forms substitute for the hulkhead,
more Or less perfect according To the nature
of the soil. Now and then, to be sure in
fact, every day-a little air will blow ont
and water and sand enter the tunnel, but
Immediately, instead of running away from
the danger, the efforts of all are turned to-