IIRC Mulholland was not an engineer and some grievous engineering errors had been made on that project.
An older relative worked on the John Hancock Building and I heard ALL about it. Interesting stuff!
Short version:
August 24, 1966 – Developers of the 100-story John Hancock Center at Michigan Avenue and Delaware Place announce that they have ordered a second round of tests for 57 caissons, a portion of the caissons that will form the foundation of the building. The action comes after voids and imperfections are found in five of those caissons, starting about 60 feet below ground level. Engineers predict that testing and repairs will continue for three weeks. Construction on the super-tall building was halted on August 5 when a caisson moved sideways after a 12-ton test beam was placed on top of it. J. Theodor Dailey, a co-developer on the project, says, “Such a review is necessary because of the unique design of the building, its foundation, and soil conditions at the site. When approved, the foundation will have undergone one of the most complete analysis in construction history.” [Chicago Tribune, August 25, 1966]. 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. Over two-dozen of the caisson holes required corrective work, adding six months to the construction schedule and another $1 million to the budget. It is fortunate, though, that the problems were discovered and corrected. Considering what might have happened if the problems were not detected, the Engineering News-Record opined, “Cost in dollars or in lives from damage that might have befallen a completed 100-story John Hancock Center if its faulty caissons had settled years hence is just too horrible to dwell upon.” [Chicago Tribune, March 24, 1985]
<><><> 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...
<><><> IIRC Mulholland was not an engineer and some grievous engineering errors had been made on that project. <><><>
Roger!
Mulholland was self taught.
The dam was attached to the earth, and on one side, that earth turned out to be just a giant boulder, sitting ON the bedrock, rather than being an extension of the bedrock.
The dam’s height was increased twice, creating a much greater surface area, and therefore increasing a (future) fatal pressure on the dam, which caused the giant boulder (the dam’s shoulder) to move enough to fracture the dam.
Bodies were washed downstream, with some reaching the Pacific Ocean.