The St. Louis Republic. [volume] (St. Louis, Mo.) 1888-1919, 1901-03-17
Superiority of the American
System. The st. Louis and
Brooklyn Bridges.

Bridges must have foundations for their
piers. Up to the middle of the Ninteenth
Century engineers knew no better way of
making them than by laying bare the bed
Of the river by a pumped-out cofferdam, or
by driving piles into the sart;. as Julius
Caesar did. About the middle of the CEN
fury a French engineer conceived the first
plan of a pneumatic foundation. which led
to the present system of COMPRISING air by
pumping 1t into an inverted box. called q
c%aisson. with air locks on top to enable men
and materials to go in and out. After the
soft materials were removed, and the calls
son sunk by its own weight TO the proper
depth. 1t was filled with concrete. The limit
Of depth is that in which men can work in
compressed air without injury, and this is
not much over 100 feet.
The foundation of the Brooklyn and St.
Louis bridges were put down In this man
ner.
In the construction Of the PoughkeepsIe
bridge over the Hudson in 1873, 1t became
necessary to go down 135 feet below tide
level before hard bottom was reached.
Another process was invented to take the
place OF compressed air. Timber caissons
were built. having double sides. and the
spaces between them filled with stone to
give weight. Their tops were left open and
the American single-bucket dredge was
SSN 80 obShSk q { anu u
by a very long wire rope worked by the
engine. and with 1t the soft material was
removed. BY moving this bucket to differ
ent parts Of the caisson its sinking was
perfectly controlled. and the caisson final
ly placed in its exact position. and per-
fectly vertical. The internal space was
then filled with concrete laid under water
by the same bucket, and leveled by divers
when necessary.
While this work was going on. the Gov
eminent Of New South Wales in Australia
called for both designs and tenders for a
bridge over an estuary of the sea called
Hawkesbury. The conditions were the
same as at Poughkeepsie. except that the
soft mud reached to a dept of 100 feet be-
low tide-level.
The designs of the engineers of the
Poughkeepsie bridge were accepted. and
the same method of sinking open caissons
Din this case made of from was carried out
with perfect success.
The erection of this bridge involved an
other difficult problem. The mud was too
soit and deep for piles and staging, and
the cantilever system in this site would
have increased the cost.
A staging was built on a large pontoon
at the shore, and the span erected upon 1t.
The whole was then towed out to the bridge
site at high tide. AS the tide fell, the pon-
toon was lowered and the steel girder was
placed gently on its piers. The whole OPP
Grafton was completed within six hours.
The other five spans were placed in the
same manner.
The same system was followed after
wards by the engineer Of the Canadian Pa
ciic in placing the spans OF n bridge over
thu 81, Lawrence. IN a very rapid current.
u 1. now used in replacing old spans by now
rncs. az 1t interrupts traf1c for the least
# 'tie time.
The solution of the problems presented at
gave the second Introduction
If American engineers 10 fridge l. -ins
outside of America, The first was in 17S6,
When An American carpenter Or sliipwrigat