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2016 Vol.32, Issue 8
Assessment of Impact-echo Method for Cavity Detection in Dorsal Side of Sewer Pipe

하수관거 배면 공동 탐지를 위한 충격반향법의 적용성 평가

Seokmin Song1
,
Hansup Kim2
,
Duhee Park3*
,
Jaemo Kang4
,
Changho Choi5
송 석민1
,
김 한섭2
,
박 두희3*
,
강 재모4
,
최 창호5
1Graduate Student, Dept. of Civil and Env. Engr., Hanyang Univ.
2Post-Doctoral Researcher, Dept. of Civil and Env. Engr., Hanyang Univ.
3Member, Associate Prof., Dept. of Civil and Env. Engr., Hanyang Univ.
4Member, ph.D. Student, Dept. of Civil and Env. Engr., Hanyang Univ.
5Member, Research Fellow, Korea Institute of Civil Engrg. and Building Technology
1비회원, 한양대학교 건설환경공학과 석사과정
2비회원, 한양대학교 건설환경공학과 박사후연구원
3정회원, 한양대학교 건설환경공학과 부교수
4정회원, 한양대학교 건설환경공학과 박사과정
5정회원, 한국건설기술연구원 지반연구소 연구위원
*교신저자. *Corresponding Author. 
31 August 2016. pp. 5-14
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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

싱크홀 발생의 주요 원인인 하수관거 배면의 공동 탐지를 위해 비파괴검사 방법 중 하나인 충격반향법을 적용한 실내 모형 실험을 수행하였다. 콘크리트 하수관의 모의를 위해 얇은 두께의 콘크리트 평판 시험체를 제작하였고 주변 지반은 모래로 조성하였으며 공동의 모사를 위해 스티로폼 박스를 모래에 매립하였다. 콘크리트 판 배면이 공동인 경우와 완전히 모래에 밀착된 경우로 나누어 실험이 진행되었으며 일정한 타격 강도의 유지를 위해 새롭게 제작된 타격 장치를 사용하여 획득 자료의 신뢰성을 높였다. 측정된 반사파는 고속 푸리에 변환과 국소 푸리에 변환을 사용하여 주파수 특성 및 시간 특성을 분석하였다. 그 결과, 푸리에 스펙트럼의 형상으로는 공동의 유무를 판별할 수 없는 것으로 나타났다. 본 연구에서는 공진 시간이라고 명한 새로운 지표를 제안하였다. 이는 공진 주파수가 일정 강도를 초과하는 지속 시간으로 정의하였다. 공진 시간은 공동의 유무를 효과적으로 예측하는 것으로 나타났다. 나아가 공동 유무를 구분할 수 있는 공진 시간을 제시하였다. 실제 현장 조건에서의 검증과 보다 광범위한 적용성의 확보를 위해 다양한 지반 조건에 대한 추가 실험과 실제 하수관에 대한 현장 실험 등을 진행할 예정이다.

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Information
  • Publisher :The Korean Geotechnical Society
  • Publisher(Ko) :한국지반공학회
  • Journal Title :Journal of the Korean Geotechnical Society
  • Journal Title(Ko) :한국지반공학회 논문집
  • Volume : 32
  • No :8
  • Pages :5-14
  • Received Date : 2015-12-10
  • Revised Date : 2016-06-07
  • Accepted Date : 2016-08-02
  • DOI :https://doi.org/10.7843/kgs.2016.32.8.5
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