A Microgravity for Mapping and Monitoring the Subsurface Cavities

지하 공동의 탐지와 모니터링을 위한 고정밀 중력탐사

  • Park, Yeong-Sue (Geology and Geoinformation Division, Korea Institute of Geoscience and Mineral Resources) ;
  • Rim, Hyoung-Rae (Geology and Geoinformation Division, Korea Institute of Geoscience and Mineral Resources) ;
  • Lim, Mu-Taek (Geology and Geoinformation Division, Korea Institute of Geoscience and Mineral Resources) ;
  • Koo, Sung-Bon (Geology and Geoinformation Division, Korea Institute of Geoscience and Mineral Resources)
  • 박영수 (한국지질자원연구원 지질기반정보연구부) ;
  • 임형래 (한국지질자원연구원 지질기반정보연구부) ;
  • 임무택 (한국지질자원연구원 지질기반정보연구부) ;
  • 구성본 (한국지질자원연구원 지질기반정보연구부)
  • Published : 2007.11.30

Abstract

Karstic features and mining-related cavities not only lead to severe restrictions in land utilizations, but also constitute serious concern about geohazard and groundwater contamination. A microgravity survey was applied for detecting, mapping and monitoring karstic cavities in the test site at Muan prepared by KIGAM. The gravity data were collected using an AutoGrav CG-3 gravimeter at about 800 stations by 5 m interval along paddy paths. The density distribution beneath the profiles was drawn by two dimensional inversion based on the minimum support stabilizing functional, which generated better focused images of density discontinuities. We also imaged three dimensional density distribution by growing body inversion with solution from Euler deconvolution as a priori information. The density image showed that the cavities were dissolved, enlarged and connected into a cavity network system, which was supported by drill hole logs. A time-lapse microgravity was executed on the road in the test site for monitoring the change of the subsurface density distribution before and after grouting. The data were adjusted for reducing the effects due to the different condition of each survey, and inverted to density distributions. They show the change of density structure during the lapsed time, which implies the effects of grouting. This case history at the Muan test site showed that the microgravity with accuracy and precision of ${\mu}Gal$ is an effective and practical tool for detecting, mapping and monitoring the subsurface cavities.

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