Laying the foundation

(Above) Portland Cement Association photo of Marina City construction site from the south in 1961. Dearborn Street Bridge under construction at left. State Street Bridge at right.

Once ground was broken, crews went to work on the foundation. As complex as Marina City was above ground, it was going to be challenging underneath, too.

In late November 1960, architectural drawings for the east tower were not complete but they were done enough for the foundation to be put in.

This mostly consisted of 80 caissons (154 counting the west tower), each buried 115 feet down, past layers of fill, gravel, three levels of water, and a variety of clays, into a limestone shelf that stretches to Niagara Falls.

Each caisson consisted of a steel tube, called a casing, which was closed at the bottom with a plug. The casing is driven into the ground to a required depth and filled with concrete, forming a “pile” inside the casing.

(Right) A caisson form laying on end on a muddy construction site in February 1961. This is a hollow cylinder that will be filled with concrete. The view is looking northeast with the State Street Bridge visible at right. Photo by Portland Cement Association.

Drilling a shaft for each caisson was “Big Bertha,” the world’s largest drill (left). Owned by Case Foundation Company, it was eight stories tall and weighed 125 tons. It could drill a hole five-and-a-half feet wide and 200 feet deep.

The maximum diameter of piles varied from 24 to 66 inches. Every 24 hours, four casings with reinforcing bars were drilled to bedrock, filled with concrete, and capped with a heavy steel plate.

This was done around the clock until March 1961.

There are three concentric rings of piles. The central core is constructed over the inner ring, but the outer rings take most of the load. The central core is 32 feet in diameter. The thickness of the core walls decreases from 30 inches at the base to 12 inches at the top, 588 feet above the base.

(Left) Aerial view of east tower foundation.

(Right) Marina City construction site, no earlier than March 1961. State Street at left. At upper right, the Dearborn Street Bridge is under construction. 80 caissons have been buried to support the east tower at upper left. The west tower will be built in the upper right corner. The platform being constructed next to the Chicago River will house commercial tenants.

With Mueser Rutledge Consulting Engineers handling the foundation engineering, the foundation consultant was Dr. Ralph B. Peck, the engineer who literally wrote the book on soil mechanics.

(Left) Dr. Ralph B. Peck. Photo obtained from The International Information Center for Geotechnical Engineers.

Peck was born in Canada to American parents, earned a Doctor of Civil Engineering in 1937, was a lab assistant to noted civil engineer Arthur Casagrande, and from 1939 to 1942, he was an assistant engineer on the Chicago Subway Project.

Since 1942, Peck had been a teacher in the civil engineering department of the University of Illinois at Urbana-Champaign. He would eventually be professor emeritus of foundation engineering at the university and known as “the godfather of soil mechanics.”

In 1948, Peck co-authored the most influential textbook in geo-technical engineering, Soil Mechanics in Engineering Practice. In 1953, he co-authored the widely used textbook, Foundation Engineering.

By February 1961 there was already a conflict with a nearby construction project. Engineers determined that caissons could not be sunk at Marina City and the new Dearborn Street Bridge at the same time. Because of soil conditions, it could damage buildings and streets. A schedule had to be worked out between the two projects. For two months in early 1961, construction of the west tower core was delayed because of work on the bridge by the City of Chicago.

(Left) Dearborn Street Bridge under construction in 1961. Marina City site at lower right.

Construction account opened with $20 million deposit

On February 16, 1961, a construction fund account was opened with $20 million at Continental Illinois National Bank and Trust Company. Interest in Marina City from prospective renters was strong around this time, with 2,000 inquiries received for 896 apartments.

The next day, the city council’s building and zoning committee heard Marina City Building Corporation’s request for a zoning change to allow it to build residences on property on which only businesses were currently allowed. Work was underway by special permit.

Written by Steven Dahlman
Presented for nonprofit educational purposes

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