Interdisciplinary and Inventive Approaches to Drilled Shaft Remediation-Paper

Paper

Pdf Summary

The paper presents a multidisciplinary approach to evaluating and remediating drilled shafts with questionable integrity. Non-destructive testing (NDT), including Cross-hole Sonic Logging (CSL) and Cross-hole Tomography (CT), is used to locate and define anomalies. Where appropriate, concrete strength estimates are derived by calibrating measured wave speeds against concrete break-strength data. Structural and geotechnical analyses then assess whether shafts can safely remain in service or require repair.<br /><br />Three case studies demonstrate tailored responses. At a Massachusetts bridge, one shaft was cored, hydro-flushed, and grouted, with CT testing before and after grouting to verify the repair. Another was strengthened with a micropile extending into bedrock. At the Mohegan Bridge, testing and analysis showed that anomalous shafts still met required capacities, avoiding substantial project delays. For New Jersey sign structures, some shafts were accepted based on estimated concrete strength, while a reinforced concrete “donut” around a shaft tip provided additional geotechnical capacity and avoided replacement shafts.<br /><br />The authors recommend a staged process: confirm anomalies with additional NDT, use CT to determine their size and location, and estimate anomalous concrete strength when useful. Apply structural and geotechnical evaluations to the as-built condition before undertaking costly repairs. Severe defects may warrant direct repair or redesign, while limited anomalies may be acceptable without intervention. The appropriate solution depends on defect characteristics, design requirements, construction conditions, and schedule. Overall, careful coordination of testing, engineering analysis, and practical remediation can preserve foundations that might otherwise be rejected while reducing cost and delay.

Keywords

drilled shafts

non-destructive testing

cross-hole sonic logging

cross-hole tomography

concrete strength estimation

structural analysis

geotechnical analysis

foundation remediation

micropile strengthening

case studies