Crosshole sonic logging (CSL) checklist for construction QA

Definition: Crosshole sonic logging (CSL) guides contractors and inspectors through access tubes, coupling, pulse analysis, anomaly mapping, and acceptance for drilled shafts, ensuring objective integrity verification and defensible records.

Plan tube layout, materials, and curing windows per specifications.
Ensure water coupling, probe calibration, and consistent scan parameters.
Analyze first arrival time and amplitude to detect defects.
Interactive, commentable checklist with export and QR code verification.

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Checklist

Crosshole sonic logging (CSL) validates drilled shaft or bored pile integrity by transmitting ultrasonic pulses between water-filled access tubes and measuring first arrival time and signal amplitude. This checklist focuses exclusively on CSL and explicitly excludes low-strain pile integrity testing (PIT). It covers tube verification, water coupling, equipment calibration, acquisition parameters, pulse analysis, anomaly mapping, and acceptance decisions. Using related methods such as ultrasonic crosshole testing terminology and sonic pulse velocity interpretation, the workflow minimizes false positives from poor coupling, ensures complete depth coverage, and produces traceable deliverables. You will confirm tube materials and sealing, equalize water temperature, establish scan increments and pull rates, monitor signal-to-noise ratio, normalize data to a baseline, and map anomalies by depth and tube angle. The outcome is a defensible accept/conditional/reject decision per approved project specifications and authority requirements. Use this interactive checklist to tick steps, add comments, attach evidence, and export PDF/Excel; a QR code secures field-to-report traceability.

Establish a repeatable CSL process from access tube verification to acceptance. Control variables that affect ultrasonic coupling, confirm equipment calibration, and document curing windows so interpretations reflect material conditions, not setup artifacts. The result is reliable, traceable integrity evidence for every shaft tested.
Use structured acquisition parameters to capture clear first arrival time and amplitude records at consistent depth increments. Real-time quality gates help crews pause to fix coupling issues, improving coverage and reducing retests, delays, and ambiguity in anomaly interpretation.
Translate pulse analysis into practical decisions by normalizing to a project baseline and mapping deviations across tube pairs. Anomaly clusters are categorized by depth and circumferential position, aligning with construction records to guide investigation, mitigation, or acceptance.
Interactive online checklist with tick, comment, and export features secured by QR code.

Pre-Test Planning and Access Tubes

1. Confirm CSL is the required method and explicitly exclude PIT from scope; align with the inspection and test plan. Acceptance: scope confirmation signed by contractor and inspector. Evidence: approved ITP, meeting minutes.
2. Review approved drawings for access tube count, spacing, and embedment depth; verify tubes reach near base and extend above cut-off. Acceptance: layout matches design. Evidence: marked drawings, site photos.
3. Verify tube material (steel or PVC), internal diameter, wall thickness, joints, and caps per approved project specifications and authority requirements. Acceptance: materials as specified. Evidence: delivery tickets, material certificates, photos.
4. Confirm tube integrity and continuity by flushing and, where accessible, passing a mandrel or borescope to check for obstructions. Acceptance: no blockage or leakage. Evidence: borescope images, obstruction log.
5. Check tube bottoms are sealed and tops fitted with watertight, ventable caps to prevent grout intrusion and air entrapment. Acceptance: no visible leaks. Evidence: close-up photos, foreman sign-off.
6. Mark tube IDs and angular positions on the head of shaft with a north reference for later anomaly mapping. Acceptance: all tubes uniquely identified. Evidence: paint marks, orientation sketch.
7. Confirm minimum concrete age or compressive strength before CSL per approved project specifications and authority requirements. Acceptance: curing window satisfied. Evidence: cylinder/break reports, strength logs.

Equipment Setup and Calibration

8. Inspect transmitter, receiver, and cables for damage; verify connectors and strain reliefs. Acceptance: equipment free of defects. Evidence: inspection checklist, photos of serial numbers.
9. Calibrate probes in a clean water bath to establish zero-offset and reference first arrival time (FAT) and amplitude. Acceptance: stable readings within specification limits. Evidence: calibration record, screenshots.
10. Set sampling rate, pulse width, gain, and filters per manufacturer guidance and project requirements. Acceptance: parameters meet specification. Evidence: instrument setup printout or screenshots.
11. Verify depth encoder or graduated cable accuracy against a physical reference. Acceptance: depth error within project tolerance. Evidence: depth check log, photo of reference.

Coupling and Water Management

12. Flush each tube and fill completely with clean, de-aerated water; remove debris and trapped air. Acceptance: water column continuous with no bubbles observed. Evidence: fill log, photos.
13. If permitted, dose an approved wetting agent to improve coupling; record product and concentration. Acceptance: additive use per specification. Evidence: batch record, product data sheet.
14. Measure and record water temperature in each tube and ambient temperature; allow equilibration time if needed. Acceptance: temperatures recorded before testing. Evidence: thermometer readings in log.
15. Perform a static coupling check by holding probes at the same depth; verify stable FAT and amplitude. Acceptance: variation within project thresholds. Evidence: QC screenshots, notes.

CSL Data Acquisition

16. Define tube pair sequence (adjacent and, if specified, diagonal pairs) and logging direction (base-to-top). Acceptance: documented test plan. Evidence: pair matrix, sequence sheet.
17. Set depth increment and pull rate to meet project resolution; confirm encoder counts match increments. Acceptance: parameters per specification. Evidence: parameter log, instrument printout.
18. Log from base to top with transmitter in tube A and receiver in tube B; record FAT, amplitude, and waveform at each increment. Acceptance: continuous coverage. Evidence: raw data files with timestamps.
19. Reverse transmitter/receiver positions and repeat the run for the same pair to cross-validate. Acceptance: differences within project thresholds. Evidence: paired datasets, comparison plot.
20. Monitor real-time signal quality; if low SNR or dropouts occur, pause to re-couple, re-flush, or adjust gain. Acceptance: restored signal quality. Evidence: before/after screenshots, field notes.

Analysis, Anomaly Mapping, and Acceptance

21. Post-process data to compute FAT, relative velocity, amplitude/energy, and waveform QC metrics. Acceptance: 100% depth coverage with valid picks. Evidence: plotted profiles, QC report.
22. Normalize results to a baseline segment and calculate deviations; apply project thresholds for significant changes. Acceptance: values within limits. Evidence: delta FAT and attenuation plots.
23. Identify anomalies where deviations persist across contiguous depths or multiple pairs; classify severity per specification. Acceptance: categorized anomaly register. Evidence: anomaly table with depths.
24. Map anomalies to plan and section using tube geometry and marked angles; issue accept/conditional/reject decision per approved project specifications and authority requirements. Evidence: signed report, data archive, QR-authenticated deliverables.

Access Tubes and Coupling Fundamentals

Successful CSL starts with reliable access tubes and stable water coupling. Tubes must match approved materials, be sealed at the base, and extend to the required elevations to ensure full depth coverage. Before testing, flush each tube, fill with clean, de-aerated water, and remove trapped air that can scatter or delay the ultrasonic pulse. If allowed, a small amount of approved wetting agent reduces surface tension and improves probe-to-water coupling. Equalize tube water and ambient temperatures and record them; temperature gradients can shift wave speed and bias first arrival time. Confirm identification and orientation marks on every tube head, including a clear north reference, so that any anomaly can be located circumferentially for construction follow-up. A quick static coupling check—holding probes at the same depth—verifies that FAT and amplitude remain stable before committing to full logging. These fundamentals reduce noise, minimize retests, and elevate confidence in the interpreted results.

Use clean, de-aerated water for stable signals.
Mark tube IDs and a fixed north reference.
Seal tube bottoms; fit tight, vented caps.
Record water and ambient temperatures.

Optimizing Acquisition Parameters and Pulse Analysis

Acquisition parameters govern data resolution and repeatability. Choose depth increments and pull rates that resolve anticipated defect sizes while meeting project productivity targets. Verify sampling rate, pulse width, and gain are set per manufacturer guidance and approved specifications; consistent settings simplify cross-comparisons. During logging, monitor waveform quality and signal-to-noise ratio. Capture first arrival time (FAT), amplitude or energy, and waveform shape at each increment. Reversed runs (swapping transmitter and receiver) help identify directional bias or coupling issues. In processing, apply consistent picking methods and normalize results to a baseline segment. Plot FAT and attenuation curves by depth and tube pair to highlight outliers. Robust pulse analysis distinguishes real material changes from artifacts caused by coupling fluctuations, providing the foundation for clear, defensible acceptance decisions.

Choose scan increments that resolve expected defect size.
Verify first arrival picking consistency.
Keep pull rates steady and documented.
Repeat scans when SNR drops.

Anomaly Mapping and Acceptance Decisions

Turning signals into decisions requires clear mapping and criteria. After identifying deviations, group them by depth continuity and recurrence across multiple tube pairs. Use tube geometry and the marked north reference to place anomalies circumferentially in plan and section views. Align findings with construction logs—cage splices, tremie interruptions, or water inflow events—to support root-cause assessment. Categorize outcomes as Accept, Conditional (monitor or investigate), or Reject per approved project specifications and authority requirements. Package results with raw data, calibration records, plots, and an anomaly register. A QR-secured report links field evidence to the final decision, supporting transparent communication with the owner and smoother closeout.

Plot delta FAT and amplitude by depth.
Correlate anomalies across multiple tube pairs.
Produce plan-view maps with tube angles.
Document acceptance with signatures and QR.

How to Use This Interactive CSL Checklist

Preparation: Assemble calibrated CSL probes, depth encoder, clean water, approved wetting agent (if allowed), thermometer, borescope/mandrel, PPE, and reporting templates. Confirm access tube layout and curing window per approved project specifications and authority requirements.
Start Interactive Mode: Open the checklist on your device, select the shaft ID, and enable tick boxes. For each step, capture photos, screenshots, and readings directly within the corresponding item.
Comment and Collaborate: Use the comment field to note anomalies, parameter changes, or coupling fixes. Mention team members to resolve issues in real time and maintain an auditable conversation.
Review and Export: Verify all mandatory items are ticked and evidence attached. Generate plots and attach calibration records, then export as PDF/Excel. The system embeds a QR code for authentication.
Sign-Off and Archive: Capture digital signatures from contractor, inspector, and owner’s representative. Distribute the export to stakeholders and archive the QR-authenticated package in the project records.

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Tatiana Ivanova Tatiana Ivanova

Jan 12, 2026

115

FAQ

Question: When should CSL be performed on a drilled shaft?

Perform CSL after the shaft meets the project’s minimum age or compressive strength and access tubes are verified sealed and filled. Testing too early risks misleading results due to immature concrete or temperature gradients. Always confirm the curing window per approved project specifications and authority requirements before mobilizing.

Question: How do I distinguish a true defect from poor coupling?

Check coupling first: flush and refill tubes, remove air, verify water temperature, and repeat a static coupling check. If deviations persist after re-coupling and appear across contiguous depths or multiple tube pairs, they are more likely material-related. Consistent acquisition parameters and reversed runs improve confidence in the interpretation.

Question: What data must be included in a CSL report?

Include calibration records, acquisition parameters, depth coverage confirmation, FAT and amplitude plots, normalized deviation plots, anomaly register with depths and tube pairs, plan/section maps, photos, and signed acceptance decisions. Export the complete, commentable package as PDF/Excel, secured by a QR code that links to source evidence.

Question: Can I use CSL results to approve or reject a shaft directly?

Yes, if acceptance criteria are defined in the contract documents. Apply the project thresholds to normalized deviations and categorize each shaft as Accept, Conditional, or Reject. For Conditional or Reject outcomes, follow the project’s prescribed actions, such as targeted investigation or remediation, before final disposition.

Question: How many access tube pairs should be logged?

Log all adjacent pairs and any additional pairs required by the project to ensure full coverage. The number of tubes and pair combinations are defined in the approved design. A documented pair matrix and complete data coverage support a defensible acceptance decision.