Application of time domain reflectometer for detecting necking defects in bored piles

This paper presents a non-destructive method for detecting necking defects in bored piles using electromagnetic waves. Small-scale laboratory experiments are conducted with a defective model pile with diameter of 0.6 m and length of 1.0 m. Four artificial necking defects are introduced on three different sides of the model pile. One necking defect is introduced at the upper position on one side of the model pile, another one is introduced at the lower position on other side of the model pile, and the other two are introduced at both the upper and lower positions on the same side of the model pile. Electrical wires are installed alongside the main rebars of a reinforcement cage to configure a two-conductor transmission line. Electromagnetic waves are generated and detected using a time domain reflectometer. The experimental results indicate clear detection of the reflected electromagnetic waves at the necking defects and pile end. In addition, the calculated defect locations are similar to the actual locations. This study demonstrates that electromagnetic waves can be effective in detecting necking defects at various positions in bored piles.