Evaluation of pile lengths using impact-induced flexural vibrations - A frequency domain approach

Abstract Non-destructive testing (NDT) techniques with impact-type excitations are often used to assess the dimension data of buried piles because such methods are generally simple in theory and relatively cost-efficient. For the evaluation of pile lengths, the feasibility of an approach relies on whether the influence due to reflected signals from the pile ends can be effectively detected and quantified. Both wave propagation theories associated with the axial and flexural waves of a slender member can be used to facilitate the length evaluation of piles, the flexural waves are the unfavorable one due to the relatively complicated dispersive nature. However, when the top of piles is inaccessible for generating longitudinal excitations, flexural behavior induced by lateral excitations still serve as a useful implement to evaluate the pile lengths. This research seeks to establish a frequency domain approach to determine the pile lengths by directly analyzing the Fast Fourier transform (FFT) spectra associated with the impact-induce flexural vibrations. The proposed procedures emphasize on developing a guideline to effectively revise the length predictions based on the phase spectra measured at two receivers with minimal reference to the tester’s subjective judgement.