Specialty Geo-Engineering in a Caisson Town-Paper

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Chicago’s skyline is founded on deep caissons and drilled shafts that bypass soft Chicago Blue Clay and bear on dense glacial till or dolomite bedrock. As buildings aged, were renovated, or needed to support new loads, restricted access and low headroom made conventional foundations difficult. Micropiles and other specialty geotechnical methods became effective alternatives for underpinning and foundation repair.<br /><br />Micropile use in Chicago expanded from small-capacity applications before 1995 to high-capacity, specified solutions. Capacities rose from under 80 kips to about 220 kips in the late 1990s, 400 kips by 2010, and 550–600 kips in more recent projects. Load testing and regulatory approvals helped advance design stresses and establish confidence in the technology.<br /><br />Case histories illustrate this development. At Orchestra Hall, micropiles enabled renovation in narrow alleys and confined basement spaces. At Navy Pier, they supplemented historic timber and caisson foundations and now support facilities including a hotel and Ferris wheel. Projects at Shedd Aquarium and Soldier Field demonstrated micropiles’ use for underpinning, new foundations, and work near fragile historic structures. At 111 South Wacker and 1845 South Michigan Avenue, micropiles reduced settlement risks associated with problematic caissons. Wrigley Field combined micropiles with drilled shafts, earth retention, jet grouting, and real-time monitoring to accommodate expansion while preserving the historic stadium. At 150 North Riverside, 600-kip micropiles provided support where conventional shafts could not fit.<br /><br />The paper concludes that micropiles and complementary ground-improvement techniques have enabled complex construction and adaptive reuse in constrained urban sites. By strengthening existing foundations and limiting disruption, these approaches can also conserve time, energy, and materials.

Keywords

Chicago skyline

micropiles

foundation repair

underpinning

drilled shafts

geotechnical methods

load testing

historic structures

ground improvement

constrained urban sites