<><><> The problems originated with the steel tubes that were used to hold back soil and water as the caisson holes were excavated. These tubes were removed as concrete was poured, which resulted in concrete being pulled up with the tubes in some caisson holes, allowing voids to form which filled with soil or water. <><><>
I worked on one of two crews installing 4,200 anchor bolts in caissons during the construction of a Mitsubishi automotive assembly plant, situated in the Bloomington - Normal area of Illinois. I’m familiar with the “steel tubes” referenced in the above excerpt. I believe the common vernacular used in the field is - caisson sleeves.
The main concern in the construction of the caissons, was soil compaction on the bottom of the caisson’s “foot”. Think of a belled shape, like an elephant’s foot.
The drilling rig used an auger bit to first establish a silo like hole in the ground, then switched bits to excavate out a bell shape cavity using a device that had triangular blades, which would extend outward from a circular housing, via rotational and centrifugal force, establishing the wider belled footprint.
An inspector would descend into the silo to test the floor soil’s compaction. Apparently, a known clay strata existed underground, which was undulating, so the drilling crew would be forced to drill down until they reached the sought after clay band. It was in this clay material, that the bell would be established.
The proposed one story building’s vertical steel columns were to be supported by these caissons. Any sidewall voids in the caissons outer concrete surfaces, due to the pulling of the sleeves, would be of some concern, but not anywhere as critical of an issue as in the construction of a 100 story building.
For this reason (comparison) I do not recall any subsequent inspections (sidewall) once the caisson floor test passed an acceptable compaction criteria.
I can only imagine the number of engineers (all) on the Hancock project that shat their pants once they discovered the anomalies in the caisson’s sidewalls.
I might (?) gather the gumption to look up the fix...
I had a tour of the plant some 20+ years ago. The place is huge. When the plant was being built it had to take a long time to grade the layout before they even put in the steel work. I live near a school that converted a baseball field to a football/track field. It probably took 4 months if not more to level out the field before even getting started on putting in the football field, stands and dressing rooms.