SuperPile(s)? Chain of Rocks Foundation Mitigation-PPT Presentation

PPT Presentation

Pdf Summary

The I-270 Chain of Rocks Canal Bridge replacement in Illinois required four piers on drilled shafts, including a 170-foot-deep shaft at Pier 4 beside the existing bridge. During drilling through loose, fine-grained soils, the excavation collapsed, creating risks to workers, the public, and the existing bridge’s pile foundations. Drilling also caused tools to be lost inside the hole, obstructing the planned shaft location.<br /><br />The team replaced the obstructed shaft with a 2-by-2 group of four 30-inch-diameter, open-ended steel pipe piles, each 150 feet long and battered away from the abandoned tools. An iterative design process balanced axial and lateral performance, drivability, pile spacing, and safe access while avoiding damage to nearby structures. All four piles underwent high-strain dynamic testing; the target resistance was 1,950 kips.<br /><br />The mitigation solution was estimated to be about as economical as the original drilled-shaft design, despite requiring a large impact hammer, a pile cap, and testing. The presentation emphasizes that driven piles can be a practical alternative to drilled shafts, that permanent casing and excavation risks near existing foundations deserve careful consideration, and that testing every pile in a group can be cost-effective. It also notes that hammer vibrations were not problematic and that small adjustments during iterative design can substantially affect performance.

Keywords

I-270 Chain of Rocks Canal Bridge

Illinois bridge replacement

drilled shaft failure

excavation collapse

open-ended steel pipe piles

pile foundation mitigation

high-strain dynamic testing

driven piles alternative

existing bridge foundations

iterative pile design