Ground Movements Caused by Caisson Installation at the Lurie Excavation Project

Lateral deformations caused by the installation of 0.76 m to 1.5 m diameter, caissons were measured by inclinometers placed at the excavation for the Lurie Research Center in Chicago, IL. The bells of the caissons were founded at an average elevation of –23.8 m Chicago City Datum (CCD). Subsurface conditions at the site and construction techniques used to install the caissons are described. Eight inclinometers were placed around the perimeter of the site and one inclinometer was placed in an ad hoc test section consisting of two caissons located in the interior of the site. The ad hoc test section and production caisson inclinometer responses are compared. The times needed to construct the production caissons around the exterior of the site and the test section caissons were very similar so that the time-dependent responses of the clays squeezing into the caisson did not cause differences in the observed responses. Larger ground movements were observed adjacent to the production caissons located near the perimeter of the temporary wall than adjacent to the two caissons located at the test section in the interior of the site. The performance data show a correlation between lateral movements caused by installing caissons and the stability number. A finite element simulation models the stress differences between the production and test section caissons. An empirical means to estimate the movements associated with caisson construction is provided.