This study analysed the mechanical behaviour of a tunnel in the vicinity of a coal-mining area using 2-dimensional and 3-dimensional analysis methods. The input parameters of the analysis were derived from in situ and laboratory rock mechanics tests. The 2-dimensional numerical analysis method revealed that the behaviour of the unsupported tunnel was influenced mainly of the distance between the tunnel and coal seam. The critical distance at which the behaviour of the tunnel is not affected by the coal seam is 1.2 ~ 1.4 times the width of the tunnel. The analysis based on the location of the tunnel, coal seam, and mined opening revealed that the in case which the tunnel penetrates the coal seam was more deformed, compared to both cases in which the coal seam exists above and beneath the tunnel. The case in which the mined opening exists above or beneath the tunnel shows more support loads acting, as well as substantial deformation occurring due to the spread plastic zone. On the other hand, results of the 3-dimensional numerical analysis methods according to various strikes and dip angles of the coal seam indicate that the behaviour of the supported tunnel is influenced more by the distance between the tunnel and coal seam rather than the direction of strike and dip angle of the coal seam. The critical distance is approximately 0.5∼0.7 times the tunnel width.
There is a growing interest in the importance of tunnels inside mountainous regions and related research due to the Korea high-speed railway project and highway line improvement project, tunnel others. In particular, the case of the tunnel excavated near a coal-mining area poses a tunnel stability problem due to specific geological conditions such as a coal seam or a mined opening. However, there are very few studies on the stress distribution and deformation behaviour of a tunnel constructed under such conditions. This study focused on a 16.2km-long loop type railroad tunnel located at the Samcheog coal field in Kangwon province, Korea. The tunnel was constructed to overcome a high difference of level in the mountainous area and solve the safety problems due to the poor condition of the railroad track and old structures. However, it is difficult to exclude the effect of the coal seam and mined opening completely, since the tunnel is located at the Samcheog coal mining area that has many abandoned mines, shafts, gangways, and crosscuts. Therefore, it is necessary to investigate the influence of coal seams and the mined opening and design a safety support for excavating tunnels in such geological condition.
The tunnel line in this tunnel area was determined through preliminary investigation (e.g., using existing data, aerial photograph interpretation, geological survey on the surface). Likewise, close investigation and survey were carried out in this tunnel line. The geological survey on the surface revealed that the valleys developed following the Osipchon fault. It is chiefly composed of sedimentary rocks and a volcanic dyke in the deep mountainous area.