Abandoned mine workings exist in many countries including in Korea and sometimes the extent of working may not be known. Most of the old mines have been worked with room and pillar method or sublevel caving method and possess great possibility of surface subsidence by failure of roof or pillar. In Korea, more than 300 coal mines and 180 non-coal mines have ceased their operations in early 1990s. These abandoned mines are giving rise to severe problem of surface subsidence because the geological layers are mostly irregular and inclined. In addition, there are many abandoned mines that have been worked at shallow depth. For these reasons, it is difficult to standardize the estimating method for subsidence in abandoned mine area and thus it is necessary to develop a new technique for the evaluation of the possibility of subsidence in every geological/mining condition. This paper describes application of fuzzy reasoning techniques to analyze the possibility of sinkhole occurrences over abandoned mines. With this new technique, authors can simplify the analyzing procedure and present the possibility of sinkhole occurrences in abandoned mine area which has a complicated geological/mining condition. Based on this, geohazard map can also be generated for particular regions over abandoned mine area.
A number of abandoned mines exist in many countries as well as in Korea. In UK, more than 70,000 old mine workings are reported and some of them may be three centuries old [1]. In the USA, 354 subsidence incidents were reported over Pittsburgh Coal bed, most of which in the form of sinkholes [2]. In 1985, Marino et al. reported that both trough and sinkhole type subsidence occurred in Illinois over shallow depth room and pillar mines [1]. After extensive study of surface subsidence in the USA [2], commented that the most prevalent subsidence features over abandoned mine land are sinkholes, with depth of sinkhole more than 3 ft, and trough or sags less than 3 ft. After studying subsidence incidents in Germany, the sudden caveins and irregular depressions in the form of sinkholes over near-surface abandoned mines have been reported and concluded that they possess a serious risk on the populated area nearby [3]. In Korea, 1,244 mines including 338 coal mines and 906 non-coal mines have been ceased operations since the early 1990s, and 9 coal mines and 723 non-coal mines are currently being worked. The subsidence problems are occurring due to the existence of abandoned mines and are commonly termed as geohazards in Korea. The sinkhole occurrence in the Boopyung graveyard was one of the examples of subsidence in Korea. It happened due to roof fall and pillar failure in near-surface openings and was restored by the sand slurry pumping into the openings [4]. Choi et al. (2004) suggested that several mining/geological parameters should be emphasized for evaluating the surface subsidence in abandoned mine area, and these parameters should be dealt with adding an extra weight in order to increase a reality in numerical analysis [5].
