The Winslow mail., 1899-04-08
MAMMOTH BUILDING.
The Vast Foundations of Chicago's
New Post Office.
One of the Greatest Superstructure,
In This Country-The Structure
Will Weigh $780,
900 Tons.

If all the materials in the recently
completed foundation for Chicago's
magnificent government building were
to be loaded on wagons, ton to each
load, and 25 feet allowed for each
wagon and team, the procession of
teams and wagons would reach 731
miles, or as far as from Chicago tc
Rochester. Gen. William Sooy-Snith.
engineer in charge of the foundation.
recently read a paper on the sub
structure at a meeting OF the Western
Society of Engineers, in which he gave
many interesting data regarding the
work that has been done he past year.
These are some of the facts:
The soil on which Chicago rests iz
loose and sandy, in general. for abott
IL feet. Then comes stratum CT hard,
brittle clay about three feet thick. Be-
low this. for so to 60 feet, there is very
soft. blue plastic clay, with spots of
sitter clay here and there and traces
Of gravel, but nowhere is the clay firm
enough to sustain any considerable
weight. At depth of from 69H to 71H
feet below the surface hardpan is
struck, and this is almost impossible to
penetrate. On account of this peculiar
nature of the soil it was decided that
the most feasible, safest and also least
expensive foundation would be one of
piles, resting upon the hardpap lime
stone.
Piles of Norway pine, 5,057 in num-
ber. and none less than 16 inches in di-
ameter at the butt and more than ten
inches in diameter at the erd, were
3riven by the powerful drivers, and
each pile driven until it required from
six to eight blows of the hammer to
1rive the pile one inch. The piles were
lriven with lower ends squared, not
sharpened, and were cut off 26% feet
below street level and 1917 feet lower
han low water level of the lake. 1t
was q nice job to cut off these tops of
piles at the required depth below, for
the trenches kept filling up with water
that oozed all too freely through the
.lay. The work, in fact, had to be
lone under water. The piles and oak
platforms bolted to their tops are thus
oerpetually immersed, insuring ever
asting durability. Fifty-nine of the
piles are driven under the place where
;he subtreasury is to be.
AS the building is to weigh not less
han 10000 tons, each pile will have
is share to perform in sustaining this
great weight But the building will be
safe. for each pile is required to uphold
out 30 tons, whereas the extreme load
t will sustain is 136.75 tons. There are
piles under London bridges over the
Thames, and also in bridges over the
Seine, which sustain weights of from co
TO 1OO tons each. When the new Chi
,ago public library was being built SO
5ons of pigiron were loaded upon the
;op of one of the piles. and the weight
stood for weeks without settlement.
Upon the tops of the groups of piles
white oak timber platforms are secure
" bolted. and upon these platforms are
oeds of fint-like concrete three feet
.hick which have undergone thorough,
searching tests. The masonry for re-
aiming walls is of Joliet and Lemont
limestone. This was laid by eight der
ticks, laying from 1000 to 1,500 cubic
feet of stone per day. In the eXcava.
ions for the basement in the center of
the lot 22,267 cubic yards Of earth were
.aken out. and in the digging of the
,uter trenches 54,294 cubic yards more
we're removed. Concrete to the extent
Of 5,122 cubic yards, 1868 board meas
ire of timber Gaping, 2S4,144 cubic
Tards of stone and 81, ,327 cubic yards
,f rubble masonry have been used.
The whole constitutes n typical pile
foundation, one in which engineers and
architects everywhere are interested,
and one which builders of edifices in
Chicago would do well to copy. There
S no danger that the new government
building will settle and crack. AGoth-
II significant fact, and one which re-
iects great credit upon the architects
and contractors, is that not one of the
surrounding big buildings-Monad-
lock, Great Northern. Marquette or
Grand Pacific-has been moved one
nch from it's place, Notwithstanding
.he heavy pile driving that has been
going on for many months. The de-
preston of part of Jackson boule-
sard, on account of the pile driving,
was because the temporary plank wall
hat had been driven in The outer side
Of the trench was not strong enough to
prevent the spongy, watery clay from
coming in to fill up the depression
caused within the fence by the pile
irfving-Chicago Times-Herald.