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    Monitoring of Two Braced Excavations in Chicago

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    The Sears Tower and Harris Bank projects, both in Chicago, involved deep basement excavation in soft clays. The Sears Tower project encompasses an area of approximately 300 by 400 ft. A concrete slurry wall forms the sides of the excavation which extends to a depth of approximately 35 to 45 ft below the adjacent street level. The Harris Bank project covers an area approximately 180 by 135 ft abutting the existing bank building. Excavation for the new building was about 45 ft deep in a 135 by 90 ft area in the southeast corner, and 30 ft deep in the remaining area. Soldier piles and lagging were used to form the sides of the excavation. The soil retention system for both projects used three levels of bracing. Corner braces and rakers extending to the interior sections of the base mat were used on the Sears Tower project. Corner braces and cross-lot struts were used at the Harris Bank project. This paper describes the apparatus and procedures used for obtaining strain data on the bracing members, and compares the measured forces with design forces in the bracing.


    excavation, bracing, strains, strain measurement, extensometers, inclinometers, temperature measuring instruments, monitors, construction, clays, soils, basements

    Author Information:

    Cunningham, JA
    Principal engineer, Soil Testing Services, Inc., Northbrook, Ill.

    Carpenter, LD
    Participating associate, Skidmore, Owings & Merrill, Chicago, Ill.

    Committee/Subcommittee: D18.23

    DOI: 10.1520/STP29176S