Omaha daily bee., 1893-05-26
FAR FROM THE LIGHT OF DAY
Great 0aisson of the New Bridge at Rest
12l Feet Below the Missouri.
DRAW PIER IS NOW soLIDLY ANCHORED
A Sixth OF n Million of the East Omaha
Bridge A. Terminal Company's Money
Permanently Placed Between Bed
rock and tho sight of Man.

rock more than 100 feet below the bed OF the
Missouri, and the order of work that mas
been so persistcntly pushed for months past
will now be reversed. Instead OF extending
the ponderous mass further downward,
every effort will now be directed tc fill
ing the hugo metal shell with concrete
and rearing its broad head of masonry per-
manently above the murky waters Of the
3ig Muddy. 1t is expected that
this will be accomplished by the
middle of next month, and that there
will then stand completed IN the center OF
the channel column that will still remain
when generations yet unborn shall have run
their earthly race and passed beyond.
1t may not be uninteresting to the people
of Omaha to know that they will soon have
here resting on that very pier, the longest
and heaviest draw span In the world. meas
ing $40 feet between centers of end-pins,
and weighing nearly 100000 pounds, while
the live load for the same will vary from 5000
to 10000 pounds to the lineal foot
But the draw span is not the only feature
of the bridge that is out of the ordinary,
for the structure in its entirety will be
revelation and an innovation.
IL Is impossible to devote mere sufficient
space to describe in detail structure OF
such magnitude, but something like an ade-
quate idea may be conveyed by q general de-
scrption of this unique product of bridge
building science.
out of High Waters Way.
IL will be what Is known as low bridge,
differing in that respect from both the struc-
lures that now span the Missouri between
this city and Council Bluffs The act of
congress authorizing its construction pro-
vides that it shall be at least ten feet above
normal high water, and in order to be be-
yond the possible reach of the surging flood
it will be even a foot higher than required.
The memorable flood of 1881 is not taken
into consideration in fixing normal high
water, but even if that height should again
be reached the water will not reach the
East Omaha bridge, but would swirl and
seeth four feet below it's huge steel
girders.
In a low bridge, the draw is. of course,
the principal feature but in this case the
engineering curiosity is the pier 1t sinks
III feet below low water, and the usual
plan of sinking caisson by work under
compressed air would have been impractical
as the pressure at that depth would be enor-
nous; in fact, work below seventy feet in
depth is attended by great fatality among
the caisson men,
New Way of Sinking Caissons.
It was to meet this condition that con-
fronted him that Chief Engineer j. A. L.
Weddell of Kansas City determined to sink
the caisson by the means of water jets, dis
charging into the sand at regular intervals
along the sharp edge of the caisson
bottom. Instead of being constructed
%'se the ordinary cdisson in Sc
ries of chambers and air locks,
this caisson, as put together in sections, re-
sembles nothing 50 much as an immense
stovepipe forty feet in diameter outside of
another twenty feet in diameter. The
smaller does not go within ten feet as low as
the outer one, but the same sheet metal con-
meets them at an angle of forty-fve degrees,
forming great funnel shaped room at the
bottom forty feet in diameter and ten feet
high and with twenty-foot circular open
ing at the top.
The space between the two great pipes
was filled with masonry above water as the
calsson was put together, the constantly in
creasing weight assisting in holding the inn
mense shell steady and carrying it down as
the thirty-two water jets washed away the
earth at the edges of the funnel shaped bot
tom. These water Jets were discharged from
pipes that ran down through the masonry
between the caisson walls at intervals Of
about four feet, the necessary pressure being
furnished by powerful force pumps
This construction of the caisson left the
inside of the smaller tube, which formed
n central shaft. entirely free and clear, but
filled OF course, with water to the height of
that in the open river outside. This pre-
cluded the possibility of any one working
at the bottom of the caisson, but there
was no necessity for anything of that
kind, as a large clamshell dredge was oper-
ated through this shaft, bringing up from
the funnel shaped space at the bottom
nearly cubic yard of earth at a load, or a
large wagon load every ten minutes. AS the
dredge excavated the center the jects cut
away at the edges, and slowly but surely the
caisson foot dropped farther and farther
from the light of day. The progress depended
naturally on the depth as we'll as on the
character of the soil that was being pep-
etrated, but during the last few weeks the
cnisson was lowered at the rate of from
three to three and half feet per day of
twenty-four hours, work being pushed day
and night.
struck Bedrock
This work has now been completed, the
bottom being reached yesterday morning and
today the caisson stands soldly on bedrock, n
great hollow tube surrounded by hundreds
OF cubic yards of solid masonry. The next
work to be done is TO fill this hol-
low center and make it rs solid and lasting
as the other. This might appear to be a
difficult feat to perform, but like many
another seemingly dinicult and dangerous
undertaking it is the simplest thing in the
world-when you know how Knowing how
In this case means the lowering into the
shaft OF large pipe with az curved arm at
the bottom and down that pipe grouting Is
dropped by wholesale, the curved arm,
which Is under control from the top
like an inverted water tower, distributing
the groutlng all over the bottom ut the will
Of the operator. This grouting hardeus
under water, and there is soon a tightly ce-
mented mass filling the great funnel 100 feet
below. Then II is that direct work may be
said to begin, for the water is pumped out
of the shaft and workmen, practically high
and dry" begin laying concrete in air more
than 100 feet below the bed of the
river. When they begin they are
surrounded by walls of masonry en-
cased in sheet iron. with plug of
grouting several feet ia thickness at their
feet keeping out the water, and the thick
ness cf this plug they constantly increase
until they reach the surface. From the
height of normal low water handsome ana
substantial stone pier rises to course of
rap stones to meet the superstructure of the
bridge. As above stated, it is expected that
by the middle of June the pier will be- en-
tirely completed, and the work of putting
inc ponderors draw span in position will be
begun
The sinking of the pier By the jet system
was much more rapid than could have been
done under the old plan, in which the open
Ing and closing Of the air locks consume a
great deal of valuable time.
breaking Records for Length.
II is not alone in its draw spau that this
bridge will prove record breaker, Tor the