Combining Multiple Techniques to Complete an Urban Deep Excavation

The William Eckhardt Research Center, a 25,500 square meter (275,000 square foot) building, was constructed on the University of Chicago campus. The structure features five floors above grade, a basement and a sub-basement. The proposed depth of excavation to construct the basement varied between 15 and 16.5 meters (49 and 54 feet). A diaphragm wall was selected as the earth retention system and permanent foundation wall due to its cost effectiveness and ability to minimize groundwater infiltration into the facility after construction. The urban, congested nature of the project location presented many design and construction challenges. The research center is located in the heart of the University of Chicago campus next to two active streets containing many utilities critical to the operation of the University, as well as two active research facilities, which house experiments that are highly sensitive to vibrations. To address these various challenges, multiple techniques were required to support each side of the excavation, including tiebacks, internal bracing, and micropile mid-span supports. The neighboring University research structures required underpinning which was accomplished using a combination of micropiles, tie downs, and jet grouting. Inclinometers and settlement points were installed and monitored throughout the braced excavation construction. The data collected showed negligible settlements, and horizontal deflections of less than 2.1 centimeters (0.8 inches) across the profile of the wall.