Evening star., 1927-10-23
HOLLAND VEHICULAR TUNNEL
HELD GREAT BOON TO TRAFFIC
Motoring Between Manhattan and Jersey
City Will Be Strikinely Expedited by
Hudson River Twin Tubes.

New York side were bored with shields
30 feet inches in dia.nete and Is
feet long. The finished tube has a
diameter of 30 feet s inches. and each
of the shields weighed 400 tons.
Each shield was divided into 13 man.
high compartments by means OF yer.
tical and horizontal partitions, and il
was In these that the workmen. slang
ly termed "sandhogs," dug out the
dirt, mud and rocks in the path OF the
shield
To keep the Hudson River out Of
the compartments the pressure of tons
or water was opposed by An equal
pressure of air within the shield In.
cessantly a struggle was waged. one
in which the air always had to main
, tain the upperhand. bat no more. Too
much air pressure could result in
blowing workmen and all up through
the bottom of the river.
Experience Of Workers.
The men who worked in this high
air pressure, before entering the shield
for work, as we'll az when leaving the
shield, had to go through a series of
air compression chambers, first to
make them used to the her air pres
the normal air pressure again. This
was done by means Of air locks, which
are connected in a series.
Going through "a series of these
locks, each of which has a higher
air compression than the predecessor,
the workmen gradually became ac-
customed to the air pressure to which
| they were subjected in the shield.
| When they quit work they went
| through these chambers in reverse
order, a much slower process, so that
| their blood would be reaccomrhodated.
| to the outside air.
While working under compressed
air the blood becomes charged with
gasses Of the air, chiefly nitrogen.
and had any workman stepped forth
suddenly into normal atmospheric
pressure his blood would literally
have boiled. He would have endured
all the agony of what doctors term
"caisson disease" and which he calls
the bends" So, each time, after
working in the shield. the workman
took As minutes or more to become
what might be termed 'decom.
pressed"
Shield Forced Forward.
When all material within reach OF
shield was pushed forward into the
draulic screws 1t took a thrust of
5000 pounds per square inch to force
the shield forward. Some days. when
going through silt, 1t went as fast as
25 feet per day, while on others II
gnawed it's way forward at a much
slower pace.
The erector, attached directly be.
hind the shield and moving forward
with 1t, picked up the heavy steel
plates and held them in position. so
that they could be riveted together,
thus forming the lining Of the tunnel.
Between the lining and the outer
earth the spaces were filled with ce.
ment and sand on the New York and
New Jersey shores. while under the
river itself the silt flowed In and
filled the spaces.
Four shields in all were used. two
| on each tunnel. working from opposite
shores. Those of the north tube met
on October %, 1924. and those OF the
south tube ON December of the same
year SO minute had been the mea-
surements and the manner in which
the shields hadf been guided that they
were in perfect alignment.
Work ON Twin Tubes Begun.
With this work completed, the inte.
rior arrangements of the twin tubes
was undertaken and along with II
was tackled one of the most serious
problems of all, that of supplying the
tubes with fresh air. No problem in
ventilation of such. a gigantic magni.
tude had ever presented itself to mod.
ern engineers and in order to solve
| this, the scientific resources OF the
United States Bureau of Mines. Yale
University and the University OF H.
linois were drawn upon. The result
has been that the Holland Tunnel.
from the standpoint OF fresh air sup.
ply, has been declared to be as safe
as any open-air boulevard.
Heretofore, for ventilation purposes
in tunnels. engineers had relied upon
the natural draft which always is pre-
sent in such a structure. This method
in short tunnel or in tunnel where
comparatively few automobiles pass, is
adequate, but as means of ventilat-
ing the Holland Tunnel this method
was. never even considered.
The tunnel primarily was con.
structed for automobile traffic, and the
exhaust of the automobile discharges
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