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Comprehensive Pile Integrity Testing: A Case Study of a Highway Bridge Foundation

Project Overview

  • Pile diameter: 1600 mm

  • Pile length: 43.5 m

  • Pile type: Bored cast-in-place pile

  • Testing methods:

    • Ultrasonic Crosshole Testing

    • Low Strain Integrity Testing

    • Core Drilling Inspection

    • Borehole Television Inspection

This case study demonstrates the application of four different non-destructive testing methods to evaluate the integrity of a large-diameter bridge foundation pile. Each method provided unique insights that collectively enabled accurate defect characterization.

1. Ultrasonic Crosshole Testing

Purpose: Evaluate pile concrete integrity
Equipment: RSM-SY7(F) Multi-channel Ultrasonic Pile Testing System

The test utilized four 45 KHz ultrasonic probes simultaneously measuring across six profiles between four access tubes. Results revealed amplitude anomalies across five profiles at 6.8-7.0m depth.

Key Findings:

  • Abnormal waveforms showed reduced initial pulse amplitude and subsequent harmonic signals

  • Normal wave velocity measurements

  • Consistent multi-profile anomalies suggested potential transverse cracking

  • Testing eliminated potential interference from tube welding defects

This method provided a full-length evaluation but has limitations in detecting:

  • Concrete outside access tubes

  • Transverse cracks

  • Thin-layered defects

2. Low Strain Integrity Testing

Purpose: Verify suspected defects
Equipment: RSM-PRT(M) Dual-channel Low Strain Tester

Using accelerometers with varied hammer frequencies and sampling intervals, tests focused on the 6.8m anomaly:

Test Sequence:

  1. Initial test: Minor in-phase reflection at 6.8m

  2. Sensor repositioning: Stronger reflection with visible secondary/tertiary reflections

  3. High-frequency impact: Clear but smaller reflection with faint secondary reflection

Conclusions:

  • Confirmed defect at 6.8m (consistent with ultrasonic results)

  • Reflection patterns suggested a significant defect

  • Superior to ultrasonics for transverse crack detection

  • Limited by soil conditions and impact energy

3. Core Drilling Inspection

Purpose: Direct visual assessment
Equipment: Standard core drilling rig

Focused examination at 6.9m revealed:

  • Discontinuous core samples

  • Inconclusive visual evidence of fracture

  • Limitations in precisely locating crack interfaces

Core Sample Observations:

  • Incomplete recovery at the suspected defect zone

  • Unable to definitively confirm fracture from cores alone

4. Borehole Television Inspection

Purpose: Visual verification of defects
Equipment: SR-DCT(W) Borehole Imaging System

The conclusive test method revealed:

  • Clear circumferential crack at 6.9m depth

  • Visual confirmation of localized fracture

  • Resolved uncertainties from other methods

Comparative Analysis of Testing Methods

Method Strengths Limitations
Ultrasonic Full-length coverage, high data density Blind zones may miss thin defects
Low Strain Good for transverse defects, simple execution Limited depth resolution, soil-dependent
Core Drilling Direct sampling, strength testing possible Limited coverage, sample quality issues
Borehole TV Direct visualization, definitive results Requires a drilled hole, localized view

Final Conclusions

  1. The pile contains a localized transverse fracture at 6.9m depth

  2. Multiple methods were essential for a comprehensive evaluation:

    • Ultrasonics identified potential anomalies

    • Low-strain characterized defect severity

    • Borehole TV provided definitive visual confirmation

  3. The fracture likely resulted from construction activities during concrete curing

  4. Core drilling alone would have been insufficient for a definitive assessment

This case highlights the importance of using complementary testing methods for reliable pile integrity assessment, particularly for large-diameter foundation elements where defects may have complex characteristics.

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