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

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Video Summary

The presentation explains why auger cast-in-place (CFA) piles were long uncommon in Chicago, despite favorable soil conditions. The city’s building code historically allowed no skin-friction capacity for piles and distinguished them from caissons, favoring established belled-caisson designs. Code changes adopted in 2019 created a path for CFA design.<br /><br />For a 27-story West Loop building, the original plan called for 66 belled caissons and six drilled shafts. Water-bearing layers made bell instability and costly remediation likely. A value-engineered design instead used 142, 30-inch CFA piles, extending into dense granular till. Load testing showed less than an inch of deflection at twice the design load.<br /><br />Implementation required addressing stakeholder uncertainty, lateral-capacity needs, load-testing requirements, a debris working platform, pile caps and chipping, tight urban access, material logistics, and winter equipment issues. Despite these challenges, construction progressed successfully, demonstrating that CFA piles can be a viable alternative in Chicago under the updated code.

Keywords

auger cast-in-place piles

Chicago building code

belled caissons

West Loop building

value engineering