ASSESSMENT, REMEDIATION AND ACCEPTANCE OF DRILLED SHAFTS THROUGH THE USE OF CSL TESTS-Paper

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The paper presents guidance for evaluating, accepting, and repairing drilled shafts with anomalies identified by Crosshole Sonic Logging (CSL). Drawing on more than 900 tests across three Costa Rican infrastructure projects, it reports that 4.9% indicated flaws. Most occurred at shaft tips, commonly due to inadequate excavation cleaning; body flaws were often linked to concrete placement delays and cold joints, while head flaws were least common and associated with concrete contamination during casing removal.<br /><br />CSL is a non-destructive method for locating and characterizing areas of potentially lower-quality concrete, not a standalone basis for rejecting a shaft. Acceptance criteria should be established before construction, and detected flaws should be assessed collaboratively by geotechnical and structural engineers using construction records, design loads, and the test’s limitations. Coring can verify concrete quality and identify false-positive CSL results. Structural analysis should determine whether the measured concrete strength can safely resist axial loads, moments, and service-level deformations. A flaw that does not impair geotechnical or structural performance may be accepted.<br /><br />Defects requiring repair are addressed according to their location. Head defects can be excavated and demolished, followed by reinforcement inspection and replacement concrete, with attention to bonding between old and new concrete. Body and tip defects are commonly repaired by pressure grouting through communicating boreholes; CSL comparisons and tomography can help assess treatment effectiveness. Repeated grouting may be needed, and ineffective repairs can require construction of additional shafts.<br /><br />The authors emphasize defining acceptance and remediation procedures in advance, considering project schedule and available technologies, and making decisions from a multidisciplinary assessment rather than CSL results alone.

Keywords

Crosshole Sonic Logging

drilled shafts

anomaly evaluation

shaft defects

concrete quality

geotechnical engineering

structural assessment

pressure grouting

acceptance criteria

foundation repair