Applicability of complex wavelet transform to evaluate the integrity of commonly used pile types

Non-destructive testing techniques are applied to evaluate the integrity of piles. The sonic echo method is usually used to determine the pile tip and the locations of defects. However, the energy of a reflected stress wave is complicated, and it dissipates quickly. It is thus often difficult to evaluate the pile integrity effectively. The purpose of this paper is to utilize the recently developed complex wavelet transform to analyze sonic echo test signals in an attempt to determine the length and location of a defect by analyzing an amplitude spectrogram and phase spectrum in different frequency bands. Several piles of different lengths, materials, cross-sections, and defects were tested to verify the proposed approach. Moreover, the discussion of the wavelet selection, the features of the wave propagation in the pile, and an explanation of the analytical steps are included. The testing results show that a complex wavelet transform can be used to evaluate the integrity of common pile types.