, 1875-09-12
1HE CUsTOM-BOUSE' TESTS.

plan We have suggested.
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1HE CUsToM-HoUsE TESTS.
The tests Of the pressure Of the Custom
House piers, under the supervision Of th'
present Government Commission, are more
thorough, and promise to be more satisfac
tory, than any that have been made hereto
fore. They are testing the capacity Of the
concrete, Of the concrete and the soil, and o1
the soil alone. In the case Of the concrete 6
pressure of twenty tons per square foot, OF
about sir times what the actual pressure will
be, has been superimposed without causing
the concrete itself to give way. This result
is to be noted with sincere qualification, for,
SO long as this enormous weight does not
| cause the slightest DETECTION in the solid con-
crete on which the building rests, there is no
possible danger Of injury to the building,
much less tottering OF the walls. In test
ing the soil alone pressure Of four tons was
made to the square foot, and it was found
| that there Was a settlement only Of II
| inches; when the pressure Was reduced to
| one-ha1f ton, it Was found that the soil re-
| covered itself about SIG Of an inch. From
this it will probably be concluded that there
! is limit to the compression of the subsoil,
which is reached when all the water has been
pressed out. After this the solid clay is left,
and no accumulation Of weight can make any
greater impression upon it than upon so
much solid rock. This was the theory OF the
local architects and the City Engineer, and
not only does it appear entirely reasonable in
itself, but tho tests of the present Con1mis~
sion seem to confirm it.
The only difficulty that presents itself in
case this theory is correct is that. the pressure
Of some piers being greater than that Of
others, it may be that the lighter piera will
not exert sufficient pressure to squeeze out
all the water in the subsoil. In such case
the heaviest piers would exert depres-
sion Of we will say, two inches,-the highest
possible compression the lighter piers
will depress, we will say, not more than one
inch, or about half as much. Then there
would be some slight cracks in the walls,
perhaps. We believe that all builders and
engineers will agree that cracks of this de-
scription cannot jeopardize the safety OF such
Titanic walls as those OF the Custom House,
resting upon solid bed Of concrete. They
may be offensive to the nice and critical eye
they may reflect upon the original architect
Of the building, and they will mar the archi-
tectural beauty Of the structure but they
will not endanger its safety. Moreover, there
is reason to believe that the continuous and
steady pressure Of the lighter piers will in
time express from the clay all the water there
is in it, and then there will be uniform set
tlement at the extreme limit, and the cracks
will disappear.
If the tests of the present Government |
Commission bear out this theory, as VIC have
reason to believe they will, there is little |
doubt but that the Commission will report !
adversely to the demolition Of the walls. We !
think that the majority Of the Commission
are satisfied that the people OF Chicago pre-
fer to confront an occasional slight crack in
the wall, or discoloration in the stone, if
the consequences are to b&n no more serious,
rather than to incur the loss Of several years
time and 81 200, 900 in money incident to the
tearing down of the walls and beginning all
over again. If the Commission, after the |
most thorough tests, become satisfied in their
own minds that the walls finished on the |
present foundation will stand securely, md
that the building will be perfectly safe
for all time, We do not doubt that
they will recommend resumption of
work. It is likely that they will, as they
should, animadvert severely upon the
stone-inspection, and the manner in which
he work has been done so far It
IS also probable that they will suggest the re-
noval of the worst stone, and tie e1action
tor the future Of better quality Of stone
han has been accepted heretofore they
nay also suggest some other valuable changes;
ont we do not believe that mere architectural
lefects that do not jeopardize the safety OF
he building will induce the present Commis-
ion to recommend sacrifice of 81, 200, 600
o remedy them.