Cross Hole Sonic Logging Versus Perimeter Sonic Logging: What Have We Learned?-Paper

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The paper compares Crosshole Sonic Logging (CSL), which uses tubes inside the reinforcing cage, with Perimeter Sonic Logging (PSL), which places tubes outside the cage to assess concrete nearer the shaft perimeter. The authors argue that PSL readings can be distorted as sonic waves pass through reinforcing steel, spacers, and other materials with different densities, making genuine concrete defects difficult to distinguish from testing noise.<br /><br />Several project case histories reported PSL anomalies that were not confirmed by coring. At the Ina Road project, PSL indicated anomalies in 35 of 76 shafts; cores from two selected shafts showed sound concrete, with compressive strengths exceeding the specified minimum. At the San Pedro River Bridge project, cores from a shaft with PSL and Gamma-Gamma Logging (GGL) indications also showed adequate concrete strength.<br /><br />A study at the Sunset Road project installed tubes both inside and outside the cages of two shafts, enabling direct CSL–PSL comparisons. PSL results were noisier and showed more apparent energy and velocity variations than CSL, including anomalies that CSL did not detect. Some GGL inconsistencies were also observed in exterior tubes.<br /><br />The authors conclude that PSL anomalies in these cases did not reliably correspond to defects and led to costly investigation and coring. They caution against applying CSL acceptance criteria directly to PSL data and recommend obtaining more evidence before using PSL as a replacement for CSL. While PSL may evaluate concrete outside the cage, its exterior tube placement can make interpretation less reliable.

Keywords

Crosshole Sonic Logging

Perimeter Sonic Logging

concrete integrity

shaft inspection

PSL anomalies

CSL comparison

gamma-gamma logging

reinforcing steel interference

non-destructive testing

foundation defects