This research has been conducted to investigate the influence of mined cavities on a tunnel to be Constructed around a coal mine, The location and dimension of cavities were supposed by analyzing synthetically geological structures and condition of coal beds as well as gangway map since there does not exist any map describing mined cavities. Detailed geological and geophysical surveys have also been carried out for the purpose ha understanding the geological structure and rock mass conditions. The two dimensional analysis with FLAC as been performed on the geological sections reconstructed from the obtained information and the effects of mined cavities on the tunnel have been assessed.


It is very difficult to know the exact location and dimension of the excavated space in coal mines since they are often not recorded in any document. In this case, it is inevitable to suppose the state of mined cavities in a second way. It may be done by estimation from gallery maps, geological structure and layout of coal beds.

The objective of this research is to investigate the effect of the ground subsidence due to milled cavities on the stability of a tunnel that is to be constructed in a mining area. The tunnel connects Yonhwadong, Tebek City and Sili, Samchok City, Gangeondo with a length of 915m.

To do this goal, geological and electrical resistivity surveys have been conducted to obtain the information about the geological structure and bed rock condition. In addition, various kinds of mining maps were collected to estimate possible dimension and location of underground cavities. Through these works geological structure around the tunnel has been established and four sections for the numerical analysis were selected.


The tunnel has a length of 915 m and passes between Yonhwadong, Tebek City and Sili, Samchok City, Gangwondo. In this area a coal mine is currently working and hence a lot of vacant spaces excavated during past several decades are largely distributed in the subsurface. Accordingly, some problems due to ground subsidence may arise on the tunnel.

The Figure 1 shows geological section that has been completed from an integration of geological

(Figure in full paper)

survey, core logging and other report (Im et al., 1993). The layers are composed of granitic gneiss, tuff and conglomerate. Geological structure is very complex because of several sets of faults as shown in the figure.


Gangways of the mine are superposed on the topographic map in the Figure 2. In the figure, a number of gangways can be seen under the tunnel. The gangways described on the map, however, are not related to the

(Figure in full paper)

mined cavities but to the transportation tunnels. Mining activities are done in the vicinity of the gangways but the exact location and the dimension of the cavities are not often plotted in the map. This implies that more numerous excavated spaces than described in the map may exist along to the gangways.

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