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Research Article

Delineation of Geological Weak Zones in an Area of Small-scale Landslides Using Correlation between Electrical Resistivity, Bore, and Well-logging Data

전기비저항 및 시추 ‧ 검층자료의 상관해석을 통한 소규모 산사태 지역의 지질 연약대 파악

Sun-Joong Lee12
,
Yu-Gyeong Kang34
,
Cheol-Hee Lee5
,
Su-In Jeon5
,
Ji-Soo Kim6*
이 선중12
,
강 유경34
,
이 철희5
,
전 수인5
,
김 지수6*
1Doctoral Student, Department of Earth & Environmental Sciences, Chungbuk National University
2Researcher, National Forestry Cooperative Federation Forest Technology Division
3Master, Department of Earth & Environmental Sciences, Chungbuk National University
4Researcher, Strategy Department, Podo Inc.
5Researcher, ASIAGEO Co., Ltd.
6Professor, Department of Earth & Environmental Sciences, Chungbuk National University
1충북대학교 지구환경과학과 박사과정
2산림조합중앙회 산림종합기술본부 연구원
3충북대학교 지구환경과학과 석사
4주식회사 포도 전략본부 연구원
5(주)아시아지오 연구원
6충북대학교 지구환경과학과 교수
*Corresponding Author
31 March 2020. pp. 31-42
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Abstract

Electrical resistivity and downhole seismic surveys were conducted together with bore investigations and well-logging to examine subsurface structures in small-scale landslides at Sinjindo-ri, Geunheung-myeon, Taean-gun, Chungcheongnam-do, Republic of Korea in 2014. On the basis of the low N-values at depths of 5~7 m in borehole BH-2, downhole seismic and electrical dipole-dipole resistivity surveys were performed to delineate geological weak zones. The low-resistivity zones (<150 Ω ‧ m) measure ~8 m in thickness and show a close depth correspondence to weathered soils consisting mainly of silty clays as identified from the bore investigations and well-logging data. Compared with weak zones in borehole BH-1, weak zones in BH-2 are characterized by lower densities (1.6~1.8 g/cm3) and resistivities (<150 Ω ‧ m) and greater variation in Poisson’s ratio. These observations can be explained by the presence of wet silty clays rich in weathered soil material that have resulted from heavy rainfall and rises in groundwater level. Downslope movements are probably caused by the sliding of wet clay that acts to reduce the strength of the weathered soil.

Keywords
landslides
electrical resistivity
downhole seismic survey
well-logging
geological weak zone

2014년 충남 태안 신진도리의 해안지역에서 일어난 작은 산사태 지역의 지하구조를 파악하기 위하여 전기비저항 및 하향식 탄성파탐사와 시추 ‧ 물리검층을 실시하였다. 시추 ‧ 검층자료에서 산사태 발생지역의 상부에 위치한 시추공 BH-2의 5~7 m 깊이에서 N값이 현저히 낮아지는 것을 확인하여 하향식 탄성파 탐사를 추가 실시하고 이 깊이에서 지질 연약대가 연장되는 것으로 가정하여 하부의 시추공 BH-1 지점까지 전기비저항 탐사를 실시하였다. 8 m 내외의 두께를 갖는 150 Ω ‧ m 이하의 저비저항 이상대는 시추 ‧ 검층자료에서 해석된 세립 실트질 점토로 이루어진 풍화토층과 잘 상관되었다. 시추공 BH-2에 걸쳐있는 지질 연약대는 시추공 BH-1에 비해 상대적으로 작은 밀도 1.6~1.8 g/cm3와 150 Ω ‧ m 이하의 비교적 낮은 전기비저항로 나타나며 포아송 비는 깊이에 따라 그 편차가 크게 나타난다. 이 지역의 산사태는 초과 강수와 이로 인한 상승 지하수면의 영향으로 물을 함유한 실트질 점토를 많이 포함하고 있는 풍화토가 전단력이 감소되어 미끄럼 활동으로 나타난 것으로 해석하였다.

키워드
산사태
전기비저항
하향식 탄성파탐사
물리검층
지질 연약대
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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 : 30
  • No :1
  • Pages :31-42
  • Received Date : 2020-02-24
  • Revised Date : 2020-03-06
  • Accepted Date : 2020-03-09
  • DOI :https://doi.org/10.9720/kseg.2020.1.031
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