Guided waves in embedded concrete piles

Results of a three dimensional (3D) guided wave evaluation of the stress waves generated by the impulse response method show that the conventional interpretation technique based on ID wave propagation theory is essentially a special application of the first branch of longitudinal wave modes with frequency components up to several thousand hertz. To extend the frequency range and incorporate special wave characteristics of higher modes so that the integrity of an embedded pile can be evaluated in a more thorough manner, a frequency-controlled method capable of exciting waveforms with higher and selective frequency components is introduced to nondestructively evaluate prototype concrete piles. Experimental results on a prototype pile are analyzed by processing the responding signals in the joint time-frequency domain, then comparing the processed waveforms with the theoretically computed results. These results show that the mode attributes of the experimentally excited waves are consistent with the results of theoretical evaluations. Based on this finding, this guided wave approach can be applied to evaluate the integrity of a drill shaft with appropriately determined parameters of the soil-pile system.