충북 증평 지질학습장 시험부지에 대한 물리탐사 및 지질공학 자료의 해석 = Interpretation of Geophysical and Engineering Geology Data from a Test Site for Geological Field Trip in Jeungpyung, Chungbuk

국문 초록 (Abstract)

지하 매질의 물리적인 성질을 정확히 평가하기 위한 가장 일반적인 방법은 해당 지점에서 시추하여 채취한 암편을 대상으로 해석한 지질공학적인 실내시험 결과와 시추공 안에 삽입한 탐사 기구를 통해 얻은 지구물리학적인 자료를 함께 복합적으로 해석하는 것이다. 이 연구에서는 충북 증평의 지질학습장으로 예정된 시험부지 중의 한 곳에서 시추공 탐사 대신 수집한 지표 탄성파탐사(굴절법 및 표면파법) 자료로부터 얻은 P파 및 S파 속도구조와 이를 토대로 작성된 포아송 비 단면을 통해 노두에 좁은 폭으로 드러난 암석 환경(적색퇴적암, 회색화산암, 풍화 화산암) 및 접촉선에서 관찰된 단열, 파쇄대가 확인되는지 알아보았다. 또한 탐사 지역에 주로 분포하는 회색 화산암과 적색 퇴적암을 대상으로 지표지질 조사와 실내 지질공학 실험을 수행하였다. 탐사자료에서 평가된 동적 탄성계수 영률은 지질공학 자료의 정적 탄성계수보다 높았다. 실내 시험에서 회색화산암에 비해 공극률이 작고 함수비가 작은 것으로 평가된 적색퇴적암은 추가적으로 건기와 우기에 실시한 전기탐사(비저항 및 자연전위) 결과에서 건우기와 관계없이 상대적으로 전기비저항이 높고 그 변화 폭이 매우 작은 영역으로 확인되었다. 특히 높은 함수비와 공극률을 갖는 풍화된 회색 화산암과 함께 접촉선에서 좁게 발달한 단열 파쇄대가 우기 때의 충전율을 높이는 열린 통로의 역할을 한 것으로 해석된다.

다국어 초록 (Multilingual Abstract)

The best way of investigating the physical and mechanical properties of subsurface materials is the combined interpretation of data from borehole geophysical surveys and geotechnical experiments with rock samples. In this study two surface seismic surveys with refraction and surface-wave method are alternatively conducted for downhole seismic surveys in test site for geological field trip in Jeungpyung, Chungbuk. P- and S-wave velocity structures are delineated by refraction and MASW (multichannel analysis of shear waves) methods, respectively. Possion’s ratio section, reconstructed from P- and S-wave velocities, is correlated to the outcrop geological features consisting of reddish sedimentary rock, gray volcanic rock, and joints/fractures. In addition, rock samples representative for reddish sedimentary and gray volcanic features are geotechnically analyzed to provide physical, mechanical properties, and elastic modulus. Dynamic elastic moduli estimated from geophysical data is found to be higher than the one from geotechnical data. Reddish sedimentary rock characterized with low porosity and moisture content corresponds to the zone of low electrical resistivities and their small variations in the resistivity sections between the rainy and dry days. This trend suggests that the weathered gray volcanic rock and the nearby fractures with higher low porosity and moisture content are interpreted to be good carrier especially in rainy season.

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