Time–frequency analyses of pile-integrity testing using wavelet transform

Detecting pile-integrity is an important topic for civil engineers and researchers. The pile-integrity testing signals acquired from the receivers on pile heads will tend to be complicated, as defects and undesired background vibrations exist. In this paper the continuous wavelet transform (CWT) method, with time–frequency distribution, is adopted to enhance the characteristics of the testing signal in order to improve the identification ability in both numerical simulations and experimental cases. The results indicate that testing signals can be displayed in the time–frequency domain at the same time and then be explored every single time by CWT, especially for changes in frequency content. In addition, CWT tends to reinforce the traits and makes all the information more visible. The feasibility of combining CWT with the sonic echo (SE) method is demonstrated. This approach is easily and quickly interpreted, and the pile-integrity is proven as well.