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http://dx.doi.org/10.7843/kgs.2016.32.8.5

Assessment of Impact-echo Method for Cavity Detection in Dorsal Side of Sewer Pipe  

Song, Seokmin (Dept. of Civil and Env. Engr., Hanyang Univ.)
Kim, Hansup (Dept. of Civil and Env. Engr., Hanyang Univ.)
Park, Duhee (Dept. of Civil and Env. Engr., Hanyang Univ.)
Kang, Jaemo (Dept. of Civil and Env. Engr., Hanyang Univ.)
Choi, Changho (Korea Institute of Civil Engrg. and Building Technology)
Publication Information
Journal of the Korean Geotechnical Society / v.32, no.8, 2016 , pp. 5-14 More about this Journal
Abstract
The leakage of water under sewer pipelines is one of main sources of sinkholes in urban areas. We performed laboratory model tests to investigate the presence of cavities using impact-echo method, which is a nondestructive test method. To simulate a concrete sewer pipe, a thin concrete plate was built and placed over container filled with sand. The cavity was modeled as an extruded polystyrene foam box. Two sets of tests were performed, one over sand and the other on cavity. A new impact device was developed to apply a consistent high frequency impact load on the concrete plate, thereby increasing the reliability of the test procedure. The frequency and transient characteristics of the measured reflected waveforms were analyzed via fast Fourier transform and short time Fourier spectrum. It was shown that the shapes of Fourier spectra are very similar to one another, and therefore cannot be used to predict the presence of cavity. A new index, termed resonance duration, is defined to record the time of vibration exceeding a prescribed intensity. The results showed that the resonance duration is a more effective parameter for predicting the presence of a cavity. A value of the resonance period was proposed to estimate the presence of cavity. Further studies using various soil types and field tests are warranted to validate the proposed approach.
Keywords
Sewer pipe; Cavity detection; Nondestructive testing; Impact-echo; Signal processing; Resonance duration;
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