A Comparison of Non-Destructive Integrity Tests on Experimental Drilled Shafts-Paper

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The study compared Crosshole Sonic Logging (CSL) and Thermal Integrity Profiling (TIP) on four full-scale drilled shafts at Oregon State University. The shafts varied in reinforcement and casing: a baseline shaft with mild steel reinforcement (MIR), one with high-strength reinforcement (HSIR), a cased shaft with internal reinforcement (CIR), and a cased shaft with almost no internal reinforcement (CNIR).<br /><br />CSL tests found no significant defects in any shaft. Minor reductions in signal velocity or energy occurred at some depths and were attributed mainly to access-tube couplers, construction details, or pre-installed voids for lateral-loading equipment. CSL performed through HSIR’s hollow, fully threaded steel reinforcement bars produced cleaner, more easily interpreted signals than tests using roughened PVC tubes. The results support using these bars as both structural reinforcement and CSL access paths.<br /><br />TIP measurements were collected for MIR, HSIR, and CIR; no TIP data were collected for CNIR. TIP likewise indicated sound, continuous construction. It also estimated shaft radius with depth and revealed cage alignment and concrete cover. MIR’s cage was slightly off-center but retained adequate cover; HSIR and CIR cages were well centered. The estimated radius variations reflected changes in soil conditions and are expected to help interpret future axial and lateral load tests. Casing affected temperature readings, including possible insulation from an air gap near the ground surface, but did not prevent useful interpretation.<br /><br />The methods provide complementary information: CSL assesses concrete quality along paths between access tubes, while TIP can indicate shaft geometry and cage position. TIP did not detect the small pre-fabricated voids identified by CSL, illustrating that the methods have different detection capabilities. Overall, both tests judged the shafts to be free of serious anomalies, and hollow threaded bars proved effective for CSL testing.

Keywords

Crosshole Sonic Logging

Thermal Integrity Profiling

drilled shafts

Oregon State University

concrete quality

reinforcement

casing effects

shaft geometry

hollow threaded bars

nondestructive testing