Integrity Testing of Bored Piles Using Sonic Logging

A power plant is being founded on bored concrete piles which penetrate 30–40 m of compressible soil and are socketed into rock. An integrity testing program of these cast‐in‐place piles included shaft coring, compression testing of concrete cores and geophysical sonic logging of core holes. Sonic logging along the core hole was performed with a downhole probe containing a 40 kHz transmitter and multiple receivers. The intensity (attenuation) of the sonic signal has been shown to be a more reliable indicator of concrete quality than P‐wave velocity. By normalizing the intensity of the energy arrival against the maximum intensity observed in the pile being tested, a correlation with concrete compressive strength as measured by core crushing was identified. Finally, the use of multiple pipes cast into piles has been shown to be an effective way to test piles without coring. This technique permits performance of both near‐field and cross‐pile testing to evaluate the majority of the shaft area.