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Research Article

Crossplot Interpretation of Electrical Resistivity and Seismic Velocity Values for Mapping Weak Zones in Levees

제방의 취약구간 파악을 위한 전기비저항과 탄성파속도의 교차출력 해석

Kyoung-Seo Cho12
Jeong-In Kim1
Jong-Woo Kim3
Ji-Soo Kim4*
조 경서12
김 정인1
김 종우3
김 지수4*
1Master Student, Department of Earth & Environmental Sciences, Chungbuk National University
2Researcher, ASIAGEO Co., Ltd.
3Professor, Department of Civil Engineering, Cheongju University
4Professor, Department of Earth & Environmental Science, Chungbuk National University
1충북대학교 지구환경과학과 석사과정
2(주)아시아지오 연구원
3청주대학교 토목공학과 교수
4충북대학교 지구환경과학과 교수
*Corresponding Author
31 December 2021. pp. 507-522
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Abstract

각 탐사의 반응 값은 지하 매질의 특정 물성에 따라 달라지기 때문에 한가지의 지구물리학적 방법만으로는 탐사목적을 달성하지 못하는 경우가 종종 있다. 특히 지질재해 위험에 취약한 지역을 조사하는 경우, 인명 및 재산피해를 최대한 줄이기 위해 한 가지 이상의 탐사방법을 사용하는 것이 효과적이다. 제방의 안전성 평가를 위한 이 연구에서는 각 탐사결과들을 개별적으로 해석하는 대신 탄성파속도(굴절법에 의한 P파속도와 MASW의 S파속도)와 전기비저항 값들을 통계적으로 분석하여 결정된 임계값들을 기반으로 취약구간과 안전구간 등으로 구분하는 사분면 상관기법을 수행하였다. 임계값은 수평 4층 구조와 경사진 파쇄대에 대한 모델자료를 가지고 수행한 사분면 상관기법을 테스트하는 과정에서 두 개의 속성자료 모두 평균에서 표준편차를 빼준 값으로 결정되었다. 전기비저항-P파 속도의 교차출력에 비해 전기비저항과 S파속도를 이용한 교차출력 해석이 제방 시스템의 토양유형, 지반강성 및 암석학적 특성 정보를 보다 충실히 제공하였다. 낮은 S파속도와 높은 전기비저항으로 2사분면에 투영된 느슨한 모래 구역이 취약구간으로 평가되는데 이와 같은 해석은 시추공 표준관입시험에서 보인 중심코어의 N 값 분포로 뒷받침되었다.

키워드
교차출력 해석
제방 취약구간
전기비저항
탄성파속도
지반강성

Specific survey objectives often cannot be met using only one geophysical method, as each method’s results are influenced by the specific physical properties of subsurface materials. In particular, areas susceptible to geological hazards require investigation using more than one method in order to reduce risks to life and property. Instead of analyzing the results from each method separately, this work develops a four-quadrant criterion for classifying areas of levees as safe or weak. The assessment is based on statistically determined thresholds of seismic velocity (P-wave velocity from seismic refraction and S-wave velocity from multichannel analysis of surface waves) and electrical resistivity. Thresholds are determined by subtracting the standard deviation from the mean during performance testing of this correlation technique applied to model data of four horizontal and inclined fracture zones. Compared with results from the crossplot of resistivity and P-wave velocity, crossplot analysis using resistivity and S-wave velocity data provides more reliable information on the soil type, ground stiffness, and lithological characteristics of the levee system. A loose and sandy zone (represented by low S-wave velocity and high resistivity) falling within the second quadrant is interpreted to be a weak zone. This interpretation is well supported by the N values from standard penetrating test for the central core.

Keywords
crossplot analysis
levee weak-zone
electrical resistivity
seismic velocity
ground rigidity
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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 : 31
  • No :4
  • Pages :507-522
  • Received Date :2021. 10. 05
  • Revised Date :2021. 12. 02
  • Accepted Date : 2021. 12. 10
  • DOI :https://doi.org/10.9720/kseg.2021.4.507
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