Evening star. [volume] (Washington, D.C.) 1854-1972, 1930-05-18

ers Of I-beans, which weigh 14.76
pounds q foot; are welded on 13-inch
centers across the narrow dimension OF
each pan. These take the thrust of
the shield jack as 1t moves forward
Each segment weighs about 1000
comprise q complete ring of lining. AS
the shield progresses, these Innings are
erected and bolted. the joints between
each successive ring and between each
segment Of each ring being water
PROCEED.
80 Hydraulic Jacks Used.
Spaced around the circumference of
the shield machine are 80 150-ton
the lining rings, shove the shield for
ward, making moves Of az feet. AS
each forward thrust is made the jacks
are released and a q. foot steel ring
is bolted into position to act as the
lining. There are four working plat
forms"
So accurate were the engineers in
Judging the underground operations
that they were able to steer the power
full machine right into the submerged
steel tunnel that had been placed in
the river. After the Detroit side had
been bored out, the great machine was
side.
The completed tunnel will have road
ways % feet wide. with an overhead
clearance of IA feet The width will
permit the operation OF two traffic
lines. one in either direction. with an
additional lane In case Of emergency.
This permits of q traffic capacity of
1000 motor cars an hour in each
direction.
u1.L~,-4. ,.Ioz. o.n t.~;n~ 49, a., Ro,.
the expeditions handling OF the heavy
trafic. The same methods that have
been tried and found satisfactory in
the Holland Tunnel are to be adopted.
Disabled cars will be removed with
split second dispatch, safeguarding every
minute of the swiftly moving caravan
Of underground travellers.
Two Plants VentiIate Tube.
An ADEQUATE supply Of pure air is
insured by the two powerful ventilat-
ing plants on opposite sides of the river.
Fact structure is ITO feet and so by 80
feet in area. There are about 5000
glass lowers through the vents OF
which fresh air Is drawn by blowers
and forced up from under the roadway
OF the tunnel. The vitiated air and ex-
hauSt gases are drawn up through the
ceiling of the tunnel, driven back to
the ventilating plant and expelled
through two small stacks. There is a
battery of IL 12-foot fans in each plant,
providing sufficient capacity to change
/ 900 600 cubic feet Of air in the tunnel
every 30 seconds.
Thus every minute and half all
the air in the long tunnel will be COM
pletely changed. To safeguard against
any emergency, so per cent excess blow
err and fan capacity is being provided IN
each ventilation plant.
Although the Detroit Canada Tunnel
parallels in many respects to the Hol-
land tubes, they differ widely. The
Holland Is nearly two miles in length,
has two lanes In each of the two tubes,
which were bored by shield and drilled
through rock and river muck at a cost
of $48 100000. Thanks to the hard
clay substance in the bottom Of the
Detroit River, engineers had a lucky
break, which saved the tunnel owners
millions of dollars and permitted adopt
ing the unique submerging plan for
sinking the 10 Segments.
Crude Methods Recalled.
The efficiency Of the modern tube
builder contrasts strikingly with the
methods first used in tunneling into
the earth. Eighteen centuries ago,
when the Romans built their most
lhInOuS buAiAACt, tapping hdAc SCidLAO
IL years were needed, and an army of
80 900 men was used up-literally used
up-in the project. Slaves and mill
tarv prisoners were sent into the work.
inEs to throw water upon the rock
strata, which had been superheated by
long burning fires, amid they died by
the hundreds.
Again and again water carriers failed
TO emerge. Through the choking air
they penetrated until they were close
to the rock face, and then cast their
water against that glowing surface
Instantly vast clouds of steam rushed
at them and only the agile escaped
scalding.
Their cries were mingled with deaf
ering reports as the rock cracked and
split under the sudden contraction.
The murky light of torches made of
the weird scene q subterranean inferno,
and the disgers who came in to dis
lodge the debris stumbled over the
bodies OF the water men lying beside
their jars.