Developments in Thermal Integrity Testing Practice and Interpretation-Paper

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The paper reviews advances in thermal integrity testing (TIP) for deep foundations, focusing on distributed fibre optic sensing (DFOS), interpretation criteria, and ways to validate test results.<br /><br />DFOS measures temperature along fibre optic cables attached to foundation reinforcement during concrete curing. Compared with earlier probe- and thermistor-based systems, it provides frequent, continuous measurements and is robust in construction conditions. It can also be used in low-cut-off piles and foundations with limited concrete cover.<br /><br />TIP, like cross-hole sonic logging (CSL), identifies anomalies by comparing measured results with the expected profile rather than relying on a single absolute value. Normal measurement and sensor-position variability can produce temperature differences of around ±2°C; significant deviations beyond this may warrant investigation. A case study showed a major temperature reduction that corresponded with a serious defect identified by CSL and construction records.<br /><br />When anomalies are unclear, investigators can use complementary methods such as repeat or alternative testing, dynamic testing, coring, or equivalent-pile-radius analysis. These methods provide useful evidence but have limitations: coring samples only a small portion of a pile, while analytical estimates of defect extent are approximate.<br /><br />The paper also presents DFOS strain monitoring during pile load tests as a way to assess how anomalies affect structural behaviour. In a case study, strain measurements corresponded with features found by TIP and CSL and with discoloration and weaker concrete in a core. The pile nevertheless performed acceptably. Such comparisons can help refine acceptance criteria, though more data and numerical modelling are needed.<br /><br />Overall, the authors conclude that fibre optic TIP is a practical, increasingly well-supported method for assessing foundation integrity. Its interpretation criteria show promise, but further validation is needed to define them rigorously.

Keywords

thermal integrity testing

deep foundations

distributed fibre optic sensing

DFOS

foundation integrity

concrete curing

cross-hole sonic logging

interpretation criteria

pile load tests

defect detection