Estimate buried metal pipe length using PZT detected stress wave reflection

A roadway guardrail, as the driver’s last safety barrier, is an important part of a transportation system. The buried depth of the metal pipe directly determines the bearing capacity of the guardrail during an impact. It is important to estimate the buried depth during the inspection of a guardrail system. In this paper, we proposed an original method by integrating wavelet denoising, multiple self-correlation analysis (MSA) and energy spectrum analysis (ESA) to estimate the length of buried metal pipe based on the stress wave reflection. The stress wave is initiated by an impact on the exposed end of the buried pipe and stress wave reflection is detected by a PZT (Lead Zirconate Titanate) transducer. To execute the proposed method, firstly, Wavelet denoising is used to process the reflected stress wave signal to improve the signal-to-noise ratio. Then, the MSA detects the major frequency of the reflected signal. At last, the ESA extracts the time interval between the reflected signal and the excitation signal with the help of Short Time Fourier Transform (STFT) that acquires the frequency band where the reflected signal is located. Experimental verifications were carried out, and two different lengths of buried metal pipes are selected to verify the feasibility of the proposed method. The experimental results indicate that the proposed method can accurately extract the length of buried metal pipes. The superiority of the proposed method over the traditional methods, such as Peak-Peak Discriminance (PPD) and Phase Analysis Method (PAM), is demonstrated by experimental comparative studies.