Vermont phÅ“nix. [volume] (Brattleboro, Vt.) 1834-1955, 1883-08-24

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 work not less
daring in conception and wonderful in exc
cution, though concealed from the eye of
the multtude-the great Hudson river tun.
mel, now in process of construction. This
remarkable effort of modern engineering sci
ence, If successfully carried out, bids fair to
equal, if not surpass, in interest and value the
triumph of Roebling. Its difficulties, proba-
bly,, arc nearly twice as great as those which
have been met and overcome in the construc.
ton of the Brooklyn bridge. The tunnel is
to be double, the two passages running paral.
lei, about twenty. five feet apart, with oonneo-
lions at intervals of about one thousand feet.
Nearly one-half mile of tunnel has already
been completed, but the width of the river at
the point chosen is such that the distance
between the bulkheads will be some o. 400
feet, and between the caissons little over
one mile, exclusive of the approaches Work
on the tunnel is, at present temporarily sus-
pended. Extreme difficulties have been met
but have been 80 far overcome az to warrant
a continuance Of the work in a short time
probably by the first of October
Before describing the tunnel and its method
of construction it might be well to state
briefly 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 "silt,"
substance which previous experience in tun.
neling has proved extremely unfavorable to
this branch of engineering One of the
chief dangers is that arising from the tre-
mendous pressure exerted by the continuous
lateral movement of largo body of silt.
| The vertical pressure of the silt can be math.
ematically computed, but the horizontal pres
sure is entirely variable Another difficulty
and danger arises from the liability of the
/ iron roof plating, by which the extension of
the tunnel is at present protected to fall in
| on the working section. and admit the water.
! This has occurred once already, but we be.
/ lieve, without loss of life. The bulkhead was
restored by the aid of workmen clad in div.
ing costume There are other minor Difficult.
ties which are constantly arising but, so far
all have been successfully met, and il is prob
able that any others, now unknown, will be
overcome by the same perseverance and sci
entihc skill already displayed.
The tunnel is being constructed by what
is known as the pneumatic process" which
may be illustrated by a tumbler held bottom
up in the air. The air in the tumbler will dis
place a certain portion of water, so as to leave
space untitled by the latter. In like man
ner, a huge caisson was first sunk it's sides
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 chiselled through, and
the tunnel commenced in lateral direction.
The walls of the tunnel are fortified, rs they
progress, with plates of boiler iron and an in
ner wall of brick and mortar The work of
tunneling has been begun on both the New
Vol nd Natv Iaru old ~ grfxr 'ba
tunuel 10 being built in sections of ten feet in
length each, protected at the ends by nova.
BILE iron bulkheads. The bulkhead is advanc.
ed from end to end of each section AS the
work advances The water which percolates
through the soil would naturally rise till it,
level was reached and fill the tunnel, we're il
not that by increasing the atmospheric pres
sure within the ca55on or tunnel by artificial
means it is kept down. The safety of the
workmen can only be secured by rendering the
tunnel air tight, ornearly So that it may hold
the air which is forced in for the the purpose
of keeping the water down to a proper level
The theory of the engineers is that the earth
in front of the side of the casson or Of the
iron bulkhead when that Is used, forms a sub
stitute for the bulkhead, more or less perfect
according to the nature of the soil Now anC
then, to be sure, in fact, every day-R little
air will blow out and water and sand enter tht
tunnel, out lmmeulhteIyi instead OF running
away from the danger, the efforts of all are
turned toward stopping the leak, which il
usually conquered in a short time.
The engineers who have this gigantic worn
, in charge confidently expect to finish it with
, in fifteen months. Its completion will mark
not only triumph of scientific skill, but
great advance in the facilities of transmission
, now enjoyed by the metropolis Through
each tunnel is to be laid railroad track
, over which trains are to pass constantly
, through one tunnel eastward aud through tn,
5 other westward. No wagon road is to b
, built, but teams will be carried through oil
cars specially constructed for that purpose
r The scheme ia one which has long been cher
, shed by engineers and advocated by capital
, lists, and sooner or later-since science ha
0 never yet been baffied in her own domain
= it must be accomplished.