Why We Specify Thermal Integrity Profiling on Every Drilled Shaft

Drilled shafts are hidden structures. Once the concrete is placed, the only way to know whether the shaft is sound is to test it. Crosshole sonic logging (CSL) has long been the standard, but it only evaluates concrete between access tubes, which leaves the cover zone outside the reinforcing cage largely unexamined.

On the Skookum Creek Bridge, we added thermal integrity profiling (TIP) to the testing program for every shaft. TIP measures the heat of hydration as the concrete cures and uses temperature probes inside the cage to build a picture of the entire cross-section, including cage alignment and the concrete cover.

The results were instructive. Of the 12 shafts, two showed a localized cover reduction that CSL alone had not flagged. Both anomalies were minor and were accepted by the engineer after review, but the data allowed us to adjust cage centralizer spacing for the remaining shafts and to document the as-built position of the reinforcement.

TIP adds about 1 percent to the cost of a shaft and requires the test within 12 to 72 hours of placement, which constrains the crew's schedule. We think it is worth it, particularly for large-diameter shafts in marine environments, where cover is directly tied to service life. We now recommend it as a standard pre-construction discussion topic for any shaft-supported structure.

Our engineering group is happy to share its shaft testing protocol and data templates with owners and designers. Contact Tomas Eriksen, our Engineering Manager, through the contact page.