Non-destructive test for pile beneath bridge in the time, frequency, and time-frequency domains using transient loading

摘要

The main objective of this paper is to evaluate the capabilities of non-destructive test (NDT) methods by using transient loading, i.e. the sonic echo (SE) method in the time domain and the impulse response (IR) method in the frequency domain, in detecting the pile length in the foundations of bridges. Methods such as these, which are based on transient elastic waves, have been used for many years. However, several drawbacks have been described in the literature, including difficulties with the installation of the testing devices. In this paper, several experimental studies were carried out on existing scoured bridge pile foundations. In order to overcome environmental limitations, the Ultrasonic Pulse Velocity method was adopted, and the installation procedure for the testing devices was modified. Moreover, a recently developed numerical signal processing tool, the Wavelet Transform (WT), was adopted to interpret the testing signal in the time-frequency domain. The results indicate that the modified testing procedure is feasible for in-service pile integrity tests. The processed signal clearly and visually illustrates the temporal changes, and the pile tip can be highlighted in the timefrequency domain. The depth of the scour pile tips can be detected precisely with the proposed modified device installation and the improved numerical signal processing. The results in the time-frequency domain are also consistent with traditional SE/IR testing methods.