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Research Article

Evaluation of the State of Rocks in Load Steps by Low-frequency Ultrasonic Flaw Detection

저주파 결함 탐지법에 의한 하중 단계에 따른 암석 내부의 상태 평가

Seong-Seung Kang1
,
Jongheuck Kim1
,
Jeongdu Noh2
,
Tae-Yoo Na2
,
Hyongdoo Jang3
,
Chin-Surk Ko1*
강 성승1
,
김 종혁1
,
노 정두2
,
나 태유2
,
장 형두3
,
고 진석1*
1Department of Energy and Resources Engineering, Chosun Univeristy
2The Research Institute of Advanced Engineering Technology, Chosun University
3Western Australian School of Mines, Curtin University
1조선대학교 에너지자원공학과
2조선대학교 공학기술연구원
3커튼대학교 광업대학
* 교신저자* Corresponding Author
March 2017. pp. 51-58
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Abstract

The purpose of this study was to quantitatively evaluate the state of rocks in load steps by using the low-frequency ultrasonic flaw detection method. The initial Vp-velocities measured with a CND tester were in the order of Z-axis < X-axis < Y-axis, with 1687.5 m/s along the X-axis, 1690.7 m/s along the Y-axis, 1548.3 m/s along the Z-axis, and an average of 1642.2 m/s. The overall average of the Q vlaues, measured with a Silver Schmidt hammer, was 62.6, which corresponds to a uniaxial compressive strength of ~105 MPa. The Vp-velocity, measured with a low-frequency ultrasonic flaw detector at load steps of 50%, 60%, 70%, and 80%, typically decreases in the order of X-axis < Y-axis < Z-axis with increasing load steps. This oder contrasts with that of the initial Vp-velocities. As the load step increases the factors that reduce the Vp-velocity in the X-axis direction are more influential than those in the Y-axis or Z-axis directions. This indicates that the initial state of rocks can vary and is dependent on the stress state.

Keywords
Low-frequency ultrasonic flaw detection
CND
Silver Schmidt hammer
Vp-velocity
Load step

이 연구는 저주파 결함 탐지법을 이용하여 하중단계에 따른 암석 내부의 상태를 정량적으로 평가하는 것이다. CND에 의한 초기 종파속도는 X축 방향 1687.5 m/s, Y축 방향 1690.7 m/s, Z축 방향 1548.3 m/s이며, 평균 1642.2 m/s로 Z축 < X축 < (≒)Y축 관계를 보였다. 실버슈미트 해머에 의한 Q값의 전체 평균은 62.6으로 약 105 MPa의 일축압축강도에 해당되었다. 저주파 결함 탐지기에 의해 측정된 하중단계 50%, 60%, 70%, 80% 수준에서 종파속도 크기는 X축 < Y축 < Z축 순으로 대체적으로 하중단계가 증가함에 따라 감소하는 경향을 보였다. 하지만, 이들 값은 초기 종파속도와 다른 경향을 나타냈다. 하중단계가 증가함에 따라 Y축이나 Z축 방향보다 X축 방향의 종파속도를 감소시키는 요인이 더 많은 영향을 미쳤기 때문으로 판단된다. 이러한 사실은 암석 내부의 초기상태는 응력상태가 변화함에 따라 다르게 나타날 수 있다는 것을 의미한다.

키워드
저주파 결함 탐지법
CND
실버슈미트 해머
종파속도
하중단계
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Information
  • Publisher :Korean Society of Engineering Geology
  • Publisher(Ko) :대한지질공학회
  • Journal Title :The Journal of Engineering Geology
  • Journal Title(Ko) :지질공학
  • Volume : 27
  • No :1
  • Pages :51-58
  • Received Date : 2017-02-17
  • Revised Date : 2017-03-03
  • Accepted Date : 2017-03-06
  • DOI :https://doi.org/10.9720/kseg.2017.1.51
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