Detecting abandoned and unknown mineshafts using microgravity survey on South Korea

We collected microgravity data for detecting abandoned mineshafts which seems to be great potential for collapse. The surveyed area used to be a mine of Cu, Zn during several decades, but after ending the running the series of collapse have been occurred in the vicinity of vertical entrance and a lot of minor collapse also have been occurred. Therefore the aim of this microgravity survey was to illuminate the shape of mineshafts and to detect the unknown development of mineshafts. We had carried out microgravity survey by CG5 gravitimeter and obtained coordinates of gravity station by Leica TotalStation. All 10 lines have about 80m in length and each line were remote about 10m and station spacings are 1m, 2m or 5m depended on how far the station located from main collapse area. All gravity data were processed by GrvPro that is automated gravity data processing program developed by author. GrvPro could produce complete Bouguer anomlies from raw data downloaded by CG5 and it had all gravity data processing tools from drift correction to several terrain correction methods. For quantitative analysis we made 3-D gravity inversion with exact terrain. The exact terrain surface was composed by DEM (Digital Elevation Model) and realistic measurement including main collapse cavity. Inverted 3-D results showed that mineshafts could be developed from the main collapsed area to southeast bound and it will be a prori information for input value for grouting in order to enhance the ground.