Terminology and Evaluation Criteria of Crosshole Sonic Logging (CSL) as applied to Deep Foundations-PDF

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The Deep Foundations Institute task force proposes updated guidance for interpreting Crosshole Sonic Logging (CSL) tests on drilled shafts. CSL can identify abnormalities in concrete, but results alone should not determine whether a shaft is accepted or rejected. Test readings may be affected by factors unrelated to concrete quality, including tube alignment, curing conditions, equipment or procedural issues, and insufficient water in access tubes; these should be checked and reported.

The paper distinguishes three terms: an <strong>anomaly</strong> is abnormal test data; a <strong>flaw</strong> is an imperfection that may not affect performance; and a <strong>defect</strong> is a flaw likely to significantly impair foundation performance. It recommends classifying each CSL profile, rather than assigning one overall rating to the shaft:

- <strong>Class A—Acceptable:</strong> First Arrival Time (FAT) increase is under 15% and relative energy reduction is under 9 dB.
- <strong>Class B—Conditionally acceptable:</strong> FAT increase is 15–30% with energy reduction under 12 dB, or FAT increase is under 15% with energy reduction over 9 dB.
- <strong>Class C—Highly abnormal:</strong> FAT increase exceeds 30%, or exceeds 15% together with energy reduction over 12 dB.

Class B and C results require assessment of their location, extent, severity, and number of affected profiles. Follow-up may include retesting, tomography, review of construction records, complementary testing, excavation, or—in more serious cases—coring and concrete strength testing.

The Engineer of Record and design team, with input from the CSL specialist, should evaluate results alongside construction and design information. Acceptance depends on the potential effect of an irregularity on structural performance, not simply on a test threshold. The authors also call for further research to better link CSL measurements with actual foundation deficiencies and performance.

Keywords

Crosshole Sonic Logging

CSL

drilled shafts

concrete anomalies

foundation defects

First Arrival Time

relative energy reduction

Class A

Class B

Class C