The Technograph.

No. 7.                  UNIVERSITY OF ILLINOIS.                1892-93.

DEEP PILE FOUNDATIONS IN CHICAGO.

By Gen. Wm. Sooy Smith, Consulting Civil Engineer, Chicago.
 

[In the preceding volume of The Techkograph was an article
by General Smith, an able civil engineer who has large experience
with foundations for heavy buildings, on the building problem in
Chicago, in which a new plan for deep foundations was proposed.
In the following article General Smith gives an account of the
method now being employed by himself in sinking one of these
foundations.—Editoes. ]

The acceptance, by the Board of Directors who are now erecting
a building for the Chicago Public Library, of a design for deep foun¬
dations for that structure, marks an era in the history of heavy
building construction in Chicago. It has for some time been evident
that the system of independent steel footings, spread or floated upon
the unstable clay which underlies the business district, is far from
satisfactory. At many points in the city small areas of the clay
surface have been tested by imposing loads to a maximum of three
tons per square foot. It has been found in this way that as the load
is increased, a proportional settlement takes place with all weights
under two to two and one-half tons per square foot, and that this
settlement apparently ceases in a short time. With rapid sinking
and with loads above two to two and one-half tons per square foot,
depending upon the location of the test, the ratio of settlement be¬
comes greater with sometimes a well marked ''point of failure," though
in every case, with the maximum load thus applied, a point has soon
been reached where the settlement apparently ceases. From infor¬
mation obtained from these tests, it has been the custom among
architects to assume 3 000 pounds per square foot as the load to be