This study shows a procedure of the geotechnical investigation, ground stability analysis and a recommendation on the ground treatment as counter-measures against coal mining subsidence in Korea. In the study area, the coal seams distribute irregularly with uneven thickness due to complex geological structure. Therefore mining works had been conducted without detail master plans. The continuous subsidence after the cease of mining works in the study area has endangered the stabilities of bridges, railway and road which call for urgent counter-measures. So, to establish a counterplan, this study was conducted in order as below,
synthesis of maps of coal mines and surface geological mapping
obtaining information from inquiries and observations
geophysical survey and boring test
review on the stability of the ground
recommendation on selection of treatment methods Geological structures inferred from the surface mapping gave useful information for estimation of the mining information about the area of insufficient and inaccurate mining map, and the results were also helpful in establishing the geological structures.
In the next step, adequate sites for geophysical surveys and boring tests were determined from the results above. And it could be inferred the locations of the cavities of shallow depth and relaxation state of the ground from the geophysical survey. And mined cavities, distribution of the coal seams as well as the geological structures were observed from the boring tests. Ground stability was reviewed with the investigation results, and as a result it was recommended that cement mortar grouting method was to be used for infilling the mined cavities to prevent residual subsidence and grouted micropile method to prevent uneven settlement.
In Korea, coal was important energy source in 1960';s to 80's, but since early 90's, coal industry has declined causing many coal mines closed.