Experimental and numerical investigation of thermal integrity profiling for bored piles with various defect types

Thermal integrity profiling (TIP) is a nondestructive testing method used to detect defects in bored piles by monitoring local temperature variations during the early stages of concrete curing. The objective of this study is to investigate the temperature responses of bored piles containing different types of defects. A field experiment is conducted using four model piles representing a sound pile, a pile with soil intrusion, a pile with necking defects, and a pile with an internal defect. Temperatures are measured using thermocouples installed along the main reinforcing bars. The measured thermal profiles show a distinct temperature reduction in the regions affected by soil intrusion and necking defect filled with soil, whereas the internal defect exhibits little thermal contrast compared with the sound pile. Validated three-dimensional finite element models are used to simulate the thermal behavior of the piles, and the numerical predictions agree well with the experimental results. Parametric studies are then performed on internal defects by varying defect size and sensor to defect distance and on necking defects by varying defect volume and filling material. For internal defects, greater thermal contrast is observed for larger defects and shorter sensor to defect distances. For necking defects, the maximum temperature difference between sound concrete and necking defects increases with both defect volume and the volumetric heat capacity of the filling material. The relationship between the maximum temperature difference and defect volume is well represented by a power function. These findings demonstrate that TIP, when combined with validated finite element analysis, is an effective method for evaluating defect characteristics in bored piles and for estimating defect volume from measured temperature data.