The Seattle post-intelligencer. [volume] (Seattle, Wash. Terr. [Wash.]) 1888-1914, 1891-01-20
rHE GREAT vANcouyEK BRIDGE
How worknen Build the Ffers Below
the Rivers Bed.


| IS taken from the West Ssors. which mag
azine profuSely Illustrated il.
The main bridge will be 4 steel structure
ESQ feet long. Beginning on the Wash
iagton side, there IS q first span OF fT5 feet.
/ followed by draw span 4tS5 feet long. with
30 feet clear on each side Of the pier. a
single span S75 feet long. four spans of s.
feet each and an end span of f75 feet The
trestle across the island viii be s,4O0 feet
III length, and the bridge across
the slough $50 feet, with e.000 foes
OF trestle beyond thst to the high
ground. This Will make continuous
length Of bridge and trestle Of two and
oue-thirG miles No detailed plan has vet
been made of the bridge across the slough,
though il viii doubtless be similar 20 the
main structure. The estimate OF 81 600 oOo
Is the cost of the bridge acroSs the river
aloue. This structure viii resemble very
much the steel bridge across the WiIlaul-
cite at Portland which was built by the
same engineers, George ;. Morrison,
of Chicago. being the chief engineer.
and George 4. Lederle resident engineer
The bridge viii be double~decked, being
thirty feet inside, and having two tracks
for trains on the lower deck and wagon
/ highway on the upper deck. The main
structure will be fifty feet from bottom TO
top and the draw Sixty-nve feet IN center
and thlrty-seyen at the ends, the bottom
OF the entire structure being forty feet
above low water aud ten feet above the
/ highest water recorded. It viii rest upon
piers sunk by means OF pneumatic eaiSSous
10 a varying depth OF from sixty to severn
/ ty-tiye feet below low water marx
The pneumatic system Of working under
water, either in the sinking of foundations
for piers or the building Of tunnels iSone
Z F..k n. n 4.
with the technlcalltieS of engineering, aud
Is fuil of interest. Ii is this work-the
sinking OF caisSons for pier foundations
that Is now going on, preparatory 70 the
erection of the superStruct0rc, which viii
he manufactured in some large bridge
building establishment in the Fast and
shipped III sections, ready 10 be put In
place upon arrival. Work Is now progress
slug on the pivotal pier for the draw.
The hrSt thing done is TO build carson,
or crib, which rs SO constructed as to
leave 4 pyFamidsl, air-tight chamber at
the bottoms III which the men can work. IL
IS made of 2Ix24, EXIT and i2xi2 timherS,
securely bolted and the cracks calked with
oakum. Around the bottom is bolted y
strip of iron, a3out two feet wide, which
serves as cutting edge when the
crib is lowered TO the bottom Of
the river. When completed enough for
sinking the crib is launched from
the ways like ship and foated out to its
position. 1t Is then sunk to the bottom
hy filling il with concrete above the air
chamber. When in place the water is ex-
PEELED from the air chamber by forcing IN
compressed air, the water being forced ous
under the edges. the weight OF the concrete
/ being sufficient 10 overcome the increased
buoyaney of the caiss0n occasioned by the
/ additional atmospheric pressure. Ii is now
ready for the work of sinking To begin.
Connection with the interior is had through
| a long, iron cylinder extending through
the caiSSCn from top 10 bottom, and pro-
| Vided with ladder rounds for ascending and
| descending. About ten feet above the air
/ chamber is n double compartment, the
/ vestibule, as IL were, of the caiSson. To
| enter the air chamber one MUST descend
! the ladder into the compartment on the left
/ and close and secure the door behind him.
/ lie then turns cock that connects with
/ the chamber below, the compressed air
| rushing in with a loud noise until the
/ atmospheric pressure Is the same as IN the
/ chamber. He can then open the door and
/ descend In returning, this process IS re-
( yer sed the compressed air from the closed
/ compartment being permitted TO escape to
| the outer air.
| In the caisson density Of two and one
4 half atmoSpheres is maintained. This sup
/ plies so much oxygen that candle burns
( with brilliant fame and can not be ex-
/ tinguished by throwing il clear across ths
| is deadened 50 that the noise OF the SHOW
/ els and picks is very slight, and the voice
/ has a dull, remote sound. To whistle -
/ impossible. The pressure upon the drum
| of the ear is very great, and some peo-
| pie can not endure II, though
| it is not specially disagreesbio
/ 10 the majority of people. The
/ men remain below two hours at time,
and work three shifts a day, q total of six
/ hours. The work goes on day and night
I by the aid OF electric lights supplied by the
| same power that runs the air condensers.
/ Most of the men employed are experienced
/ caisson workers, many Of them having
/ been brought from Memphis, whore they
/ were employed on the great bridge Mr..
| Morrison is building across the Mississippi
/ at that point.
/ The caisson is sunk by digging out the
( through the iron cylinders. Light
material. such a. sand and mud,
is sucked up through the pipe, the
/ pressure of the atmosphere being
I sufficient TO force it up after being
/ loosened by q stream OF water forced
! through a pipe and hose; but heavier
/ material such rs gravel and rock 1.-THE lat
/ ter often has 10 be blasted). IS shcveled
/ into long iron buckets and hauled up. These
/ buckets enter double chamber similar
in principle 10 the one described, but mt
i the top of the calSSon. The aperture be-
8 low IL titcH tAHScI. VIC dlE tiStAAAtttN ~ -
I cape the bucket taken ont, emptled 0k Us
/ contents into the river, and returned again
/ BY reversing the process. The escape OF
/ air from tins chamber resembles IN sound
1 and appearance the blowing of of steam
/ from boiler As the river bed IS thus dug
/ out the caIsson, with its sharp, iron edge
4 i forced down by the weight Of the con-
I crete. new timbers being added and more
/ concrete poured in as the work progresses.
/ Finally, when il has been sunk as far "a IS
/ desired. the air chamber is filled with con-
crete, as well as all the approaches 20 II,
I the result being solid pier of concrete
/ encaSed in practically lmperishahle TIM
! bers extending nfty feet below the bottom
/ of the river far enough To protect II from
/ any possible damage from hoods or shit
ing currents. Upon this huge cylinders
I FILED with concrete. are placed IS the
/ direct support Of the bridge.
/ IL may well be supposed that the plans
/ necessary for this work Is an expensive
one. ON 8 large barge lying alongside the
/ piliug is 4 complete englne-rooul, where
/ the air composers, boilers, dynaDOs, ma
I chine shop ETC. are located. Here, also,
is large dressing-room for the men, where
I they change their clothing after coming up
from below and INDUCING in cup of hot,
! strong coffee 10 fortify themselves against
| catching cold from the sudden
I change Of atmosphere. On the other
| side is long platform upon
/ which the concrete is made. This Is COM
/ posed Of basaItie sand dredged from the
! river near the mouth Of the Columbia, red
/ hssaltic rock taken from the quarry near
/ Fishers landing and crushed into small
chunks. and imported Portland cement.
These are shoveled in about equal quanti-
I +fes into a concrete mi Ner. rs here IL h tNOr-