The Salt Lake herald. [volume] (Salt Lake City [Utah]) 1870-1909, 1897-06-06

under air pressure and exeavate the
hard pan itself many feet below water
level.
The building lot was about % feet
wide by "A feet long, and it was decided
to cover over half of its entire area by
three solid masonry piers, each to sup
per. four of the II columns that carry
/ the suDerstructure. These piers were
/ constructed by the pneumatic caisson
process and work was commenced May
%, 1885, about two weeks after the I'M
derpinning was begun.
SINKING THE CAIsSoN.
A pneumatic caisson is essentially a
great diving bell, or bottomless box OF
steel or wood, underneath which the
confined air prevents the water from
rising UP inside and enables men to
work and excavate a pit into which 1t
gradually sinks far below water level
to the required depth while the ma
sorry pier is built on its top as fast as
it descends. These three caiSSonS were
q feet long. u to Is feet wide and
feet high, with solid timber walls :
feet thick and roof feet thick, covered
inside and outside with smooth heavy
plank sheathing, all we'll bolted and
spiked. and the seams caulked alright
like ships bottom, with oakum and
white lead. A heavy steel plate around
the bottom projected few inches 10
form a sharp cutting edge. Air ana
water pipes and air shafts were car
ried vertically through the roof and the
walls were extended above the roof by
water-tight planking or cofferdams
that formed an open well. When some
of the pier masonry had been pullt on
the caiSson roof to increase its weight,
the outside walls were quickly sme1red
with tallow to act as a lubricant. then
n q ha
air shafts, closed the air-tight steel
doors and commenced digging up the
bottom with pick and shovel, blasting
the powders with dynamite and load
ing the earth and stone into buckets
These buckets were hoisted by an out
side steam derrick to the top OF the
shafts where after an air tight door
had been closed below them. an upper
door was opened and permitted them
to be lifted out, emDtied into cars and
returned 20 the caisson again and so
on.
As the caisson was undermined it
sank from five TO ten feet day and as
soon as il was below water level power
full steam compressors pumped air into
the working chamber until it forced
the water out under the open lower
edges, and as the caisson sunk the
pressure was increased to a final max
inum of about 10 pounds per square
inch. This, though not sufficient TO be
Injurious to the workmen, merely
causing a considerable increase of tenn
perature and producing a sensation of |
obstruction in the ears, but if it had /
been necessary to sink the caisson /
twice or three times as far, great pre- T;
cautions would have been necessary.
The caisson was entered through an
air lock at the top of the shaft; this
was a small steel chamber large enough /
1,
tered it. They closed the alright outer I
door and opened the pressure valve; !
when the required pressure was secured I
they opened the trap door in the bot /
tom and descended the shaft into the |
eXcavating chamber of the caisson. To I
come out they entered the lock, closed /
the shaft door, opened the blow-off |
valve and when the pressure was en-
tirely relieved. opened the outer door
and emerged. 1t was necessary al
ways to increase or diminish the pres
sure very slowly and both of the lock
doors We're never opened at the same
time. either one or the other was al
ways closed and securely fastened by
the force of the caisson pressure.
When the caisson reached the hard
pan, the excavation IVES carried a short
distance into ii and the bottom levelai
and cleaned. Then concrete was low
cred in buckets and rammed down till
he whole interior of the caisson and
he holes left by the pipes and shafts
n the brick work were packed full.
rhe pier was complete below the water
evel inside the cofferdam from which
he water was pumped out, and on its
op steel beams and girders were set
% as to overhang il in both directions
md carry the columns in the required
positions at the extreme edges OF the
OF beyond where foundations could be B
placed. A solid mass of
concrete was then filed in above the