Comparing Thermal Integrity Test Data with As-Built Conditions

The use of thermistor-based methods to assess the integrity of deep foundations is increasing across the industry. There are many benefits of thermistor-based testing, which include the test results being available whilst construction works are ongoing, enabling the project team to react to any anomalies whilst the foundation contractor is still mobilised, and health and safety benefits compared to alternative methods that require instrumentation within the reinforcement cage. However, there are few case histories available which compare the thermal test data to the as-built conditions of deep foundations, which leads to the potential for misinterpretation of test results. In this paper, the thermal integrity test data from diaphragm wall panels constructed to form two deep shafts in London are presented and compared to the conditions encountered during excavation of the shafts. It is widely understood that lower temperatures during curing can indicate reductions in the concrete section, however this review of as constructed diaphragm wall panels identified that the construction process and detailing of the structural elements can also affect the temperature generated during curing of the diaphragm wall panels. This paper highlights that it is essential to review not only the thermal test outputs, but also the corresponding design and construction information. Recommendations are given as to the essential outputs required in the test report to enable this comprehensive review.