DRILLED SHAFT BASE QUALITY REDUCTIONS IDENTIFIED WITH THERMAL INTEGRITY PROFILING-Paper

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The paper examines whether Thermal Integrity Profiling (TIP) can reliably identify quality reductions at the base of drilled shafts. TIP records heat produced as concrete cures using temperature sensors attached to the reinforcing cage. Temperature measurements, combined with construction details and concrete volume, are used to create effective-radius plots and 3D models.<br /><br />Because heat naturally dissipates at the top and bottom of a shaft, these end effects must be normalized before interpreting the model. Bottom-of-shaft (BOS) adjustment uses four parameters: average temperature above the base transition, surrounding soil temperature, the BOS inflection point, and a time-dependent scale factor. Incorrect choices can distort the model or conceal defects.<br /><br />Two Midwestern bridge projects illustrate the approach. In the first, one shaft had a consistent thermal profile and effective radius, while another showed an early temperature roll-off and reduced temperature generation at its base. TIP indicated a substantial quality reduction; subsequent coring confirmed segregated concrete and limited core recovery over the lower two feet, verifying a soft toe.<br /><br />In the second project, one shaft showed an expected profile, while another displayed an early bottom roll-off, a sharp reduction in modeled radius, and low temperature generation. These findings prompted further investigation and coring. The authors also note that inaccurate estimates of concrete volume can affect radius models, especially for shafts requiring less than one truckload.<br /><br />The case histories demonstrate that, with appropriate BOS adjustments, TIP can assess shaft-base conditions as well as the rest of the foundation. Reviewing temperature-versus-time data alongside temperature-versus-depth profiles can strengthen qualitative evaluation and help identify areas requiring confirmation by coring or other investigation.

Keywords

Thermal Integrity Profiling

TIP

drilled shafts

bottom-of-shaft adjustment

quality reduction

temperature sensors

effective-radius plots

3D models

soft toe

coring confirmation