Engineering Wonders of the World
Volume I
År: 1945
Serie: Engineering Wonders of the World
Sider: 448
UDK: 600 Eng -gl.
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THE RIVER TUNNELS OF NEW YORK CITY.
105
years before—the
old Morton Street
Tunnel, now the
upper Hudson
Tunnel. That his-
toric enterprise
has the proud dis-
tinction among
New York’s river
tunnels of being
the first to be at-
tempted, and the
first of its soft-
ground tunnels to
be completed.
However, during
the long periods
when it lay-
idle, half-finished,
paralyzed either
by hopeless con-
struction difficul-
ties or by equally
hopeless lack of
money, two tun-
nels were dug
under the rock
portions of the
East and Harlem
Fig. 3.—ONE PHASE OF THE SURVEY WORK IN A TUNNEL.
The survey work, including constant checking of alignment, levels, distance out from shore,
and shape of lining, is of the utmost importance. The accuracy of "tunnel-driving depends
directly upon the frequency and exactness of the surveys. This shows a transit-man in an air-
lock, engaged in prolonging the tube centre line into the compressed-air section, a difficult
operation.
Rivers, and in one
shield method
First
Hudson
Tunnel.
of them the pneumatic
found a notable application.
We cannot better begin our
study than by a brief glance
at these two works, which
present highly instructive
similarities and contrasts.
The Croton
Aqueduct
Tunnel (Har-
lem River).
The second Croton Aqueduct, instead of
crossing the Harlem on a bridge like its pre-
decessor of forty years before,
was planned to cross by tunnel.
The shores are rocky bluffs,
and it appeared that at no
great depth solid rock would
be found across the whole width of the
river-bed. Test borings were first made, of
course, and on their showing the tunnel was
planned to be dug 150 feet below water level.
But when the contractor, after sinking his
shore shafts and starting his tunnel riverward,
had advanced but one-fourth, of the way,
he encountered soft material occupying a
depression in the rock surface. As this
tunnel was to serve as a water - conduit
under very high pressure, it was best to
have it in solid rock ; and since the water
could flow just as well at a lower level, it
was permissible to go down deeper until sound
rock was obtained. The tunnel was finally
put through successfully at a depth of 300
feet, the partly - finished drift being aban-
doned. At the great depth of the tunnel, any