BACK TO THE FUTURE, BRINGING AUGER CAST-IN-PLACE PILES BACK TO CHICAGO-PPT Presentation

PPT Presentation

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The presentation “Bringing CFA Piles Back to Chicago” traces the history of deep foundations in the city and describes their use on a 27-story residential and mixed-use project in the West Loop.<br /><br />Chicago initially relied on isolated masonry piers and timber or rail grillages. Driven piles emerged in the 1890s but caused heave and vibration, struggled to reach hardpan, and risked damage to neighboring buildings. The “Chicago Caisson”—a hand-dug, concrete-filled shaft—became a major foundation method. Later equipment sped up caisson construction, while local building-code rules limited the use of other pile types. Changes in the 2018 IBC and 2019 Chicago Building Code created a clearer path for continuous flight auger (CFA) piles.<br /><br />The project had heavy column loads and challenging subsurface conditions, including soft and stiff clays, water-bearing silt and gravel, hardpan, and bedrock. The original design used 66 belled caissons, but water-bearing layers and unstable ground created risks such as bell collapse, sidewall instability, and bottom blow-in.<br /><br />A value-engineered alternative replaced the caissons with 142, 30-inch-diameter auger-cast-in-place (ACIP/CFA) piles. These piles avoided shaft-instability problems, relied on soil bearing and extended into granular till, and provided service capacities up to 1,270 kips without requiring shafts to reach bedrock.<br /><br />Adopting the approach required broad acceptance from the owner, general contractor, building officials, structural engineers, vendors, labor, and suppliers. Other challenges included lateral capacity at the core, required load tests, working-pad conditions, pile caps and pile chipping, site constraints, and winter weather. The presentation concludes that these obstacles can be overcome, helping reintroduce CFA piles as a practical foundation option in Chicago.

Keywords

Chicago foundations

CFA piles

augur-cast-in-place piles

deep foundations

caissons

West Loop project

value engineering

subsurface conditions

building code changes

foundation engineering