Charleroi Locks: Repair Methods to Restore Structural Integrity of Large-Diameter Drilled Shafts-Paper

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The Charleroi Locks project encountered widespread weak or anomalous concrete, known as laitance, at the connection between the new river wall and its large-diameter drilled-shaft foundations. Exploratory drilling found anomalies in 85 of 86 shafts, ranging from a fraction of an inch to 24 inches thick. Because this interface transfers critical forces and experiences load reversal, analysis showed that material in defined compression zones had to be removed and the connection restored.<br /><br />The USACE established repair acceptance criteria and quality-control procedures, while the contractor developed the repair methods. After an initial demonstration revealed incomplete cleaning, the contractor refined a specialized triple-jet system. High-pressure water jets, delivered through multiple access holes, removed the laitance; down-hole video documented cleaning and guided quality-assurance reviews. The cavities were filled with zero-bleed, zero-shrinkage grout, held at 50 psi for five minutes to ensure contact with surrounding concrete.<br /><br />After curing, three verification cores per shaft, camera inspections, and grout strength tests checked for voids, interface contact, and required strength. Seventy-four shafts were repaired with grout alone. Eleven required a second grout application to address small voids. Nine could not be fully cleaned in critical zones; structural analysis found that four needed additional steel bars spanning the deficient area. Analysis indicated the repaired shafts would perform essentially as designed, with only a negligible increase in predicted lateral displacement.<br /><br />The project team successfully restored the structural integrity of all shafts. Key lessons include setting clear acceptance criteria, requiring demonstration repairs before production, using standardized documentation to manage extensive quality data, and maintaining close owner-contractor coordination throughout cleaning, verification, and repair.

Keywords

Charleroi Locks

laitance

drilled-shaft foundations

concrete repair

USACE

triple-jet system

high-pressure water jets

zero-shrinkage grout

quality assurance

structural integrity