The Washington times. (Washington [D.C.]) 1901-1902, 1901-08-18
DRIVING A Big TUNNEL.
Wonderful Modern Engineering
Methods and Apparatus.
Pneumatic Hammers and Oil FORCES
Used - Traffic Il Not interrupted.
Diving Under n Great Statue-New
YOrk's Great Underground Path.

Diving Under n GREAT Statue-New
YOrk's Great Underground Path.
The methods and mechanism used by
the contractors who are constructing the
rapid transit tunnel in this city are. In the
main. identical with those which have
been employed for years. And the excel
lence OF the work lies very largely in the
care and skill with which old IDEAS are
applied Nevertheless. there are a few in
novations. some of which nave been in
spired by local emergencies.
Where excavation has been conducted in
streets through which railways are rum
ming, most OF the digging has been done
on one side or other OF the track. But in
that part of Broadway which formerly
went by the name of the Boulevard the
workmen are taking the soil and rock
right out from under the tracks without
any interruption OF traffic. They behave
like of-the-road'' Populists. They
won't turn aside for anybody OF anything.
The device which the sub-contractor on
section 6. William Bradley. employs for
this purpose seems simple enough, and
yet ii has a rather novel application. He
uses number of trusses, which look for
all the world like so many short. stout
bridges A foot or of earth is removed
from beneath the track, enough to allow
the truss to be slipped under. The latter
is then lacked up so as to support the
rails and electric conduit. At each OF the
four corners special foundation Is con-
structed out of short timbers, crossed as
in a log cabin. The truss is now in a po-
sition where it will hold its load. and ex-
cavation can be conducted to depth Of
fifteen. twenty or twenty-five feet, accord
m he do MIR h1fp tat
to undermine the foundations of the cor
ners.
By degrees various gas pipes, water
pipes and sewers are laid bare. Before
enough soil has been removed from below
to imperil them vertical iron rods are
bolted to them and to the truss. Some Of
these rods are several feet long. And the
ducts which are thus suspended, and some
of which must be moved sideways. vary
in diameter from six to fifty-four inches.
Mr.. Bradley has something like sixty
trusses In constant use. Most of them are
of timber and present profile like very
wide. low A, but few are of steel and
are arcned- As soon as the excavation Is
finished at given point the truss Is freed
by removing the supports under mo cor
ners and it is moved along for fresh serv-
ice Eventually. it will be necessary to
cut passageway under the complicated
crossing of surface roads at Sixty-fifth
Street, and to avoid disturbing the elevat-
cd roads there, too. But neither William
Bradley, the contractor nor James Brad
ley, the foreman. seems at all apprehen-
sive about the task.
The temporary shifting of street railway
tracks is not ordinarily a difficult feat.
But where the road happens to be operat-
ed by the underground trolley system,
and the yokes and conduit have the re-
markable depth which is peculiar to this
city, such change is quite another mat
ter. Nevertheless. Holbrook. Cabot &
Daily did not hesitate to move about 500
feet of track on Fourth Avenue, Just
above Union Square. to the side of the
street. and they did so without interior
ing with the running of the cars Thereby
the contractors are enabled to work in the
middle of the avenue. Most of their dig
ginS thus far, however has been done
near one sidewalk or the other More
over. they have not been permitted to
excavate on both sides at once However.
the privilege is likely to be conceded very
soon. and teams will then be compelled
to take the centre of the avenue and to
stick to the railway tracks.
A particularly interesting. il not diff
cult, feat was performed three OF four
weeks ago at the intersection of Broad
way, Eighth Avenue and Fifty-ninth
Street In the centre of the Circle" at
that point rises a stone monument which
is surmounted by a statue of Columbus
The top of the statue is about 70 or 50 feet
above the street level, but is exactly 1M
feet above the grade which had been
adopted for the bottom of the tunnel.
And the route Of the tunnel lay under
one edge of the foundation of the monu-
ment Naughton & Co. have the contract
for this section, and they cut a way
through in short order.
Fortunately. it was not necessary to go
under the centre of the monument. At
that point. therefore, an additional found
alton of solid masonry was built.
trench was dug under the monument
abou. eight feet wide and as long as the
original concrete COMPLIMENTARY or
thirty feet at least-and deep enough to
reach to the bottom of the tunrfl. When
the new masonry had solidified it was
safe to remove the earth close to IT and
to push the tunnel alongside of it The
weight of the monument is estimated at
$50 tons, but the new masonry carried 1t
SO perfectly that undermining one edge OF
the original foundation led TO no settling
or displacement
In London and other places where there
is merely a clay soil to be penetrated II
has BEEN found advantageous to use the
Greathead shield. This is a metal cylin-
der, or ring, the front edge of which Is
sharp. and which is pushed forward hort-
zontally by powerful hydraulic jacks in
the rear. But in New York the amount
of soft earth to be removed is so small
that none Of the contractors have found
the Gre2thead system available. The old
fashioned pick and shovel are used in
stead. For rock drilling compressed air
is employed. This same agent operates
most of the hosting machines, the pumps
which remove water from the trenches
after a rain. and other apparatus. One
or two contractors use the old-fashioned
portable steam engine to conduct their
operations. but most OF them
have installed stationary engines and air
compressors at convenient points. and get
all their power from these stations. Some
times they find it necessary to transmit
the air through S-inch mains for a dis
lance of 1900 feet.
The pneumatic hammer is one of the
devices which are operated by this COM
pressed air. The invention has been en-
ployed to a limited extent in up-to-date
boiler ships and shipyards for FIVE years
or more, but is still good deal of a nov
city even in the United States. 1t is more
so in Europe. To a rubber hose, which
supplies the air. is attached slender
metal cylinder. fifteen inches or more in
length. The latter might easily be mista-